Keeler’s Chicago Crime Lab: How Polygraph Went Mainstream

Keeler's Early Life and Berkeley Roots

Leonarde Keeler was born on October 30, 1903, in North Berkeley, California [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[2]Verified Leonarde Keeler — WikiTree
Confirms birth in Berkeley, death in Sturgeon Bay, Door County, and family details including parents Charles Keeler and Louise Mapes Bunnell.. His father, Charles Keeler, was a poet, naturalist, and civic leader; his mother, Louise Mapes Bunnell, was an artist [2]Verified Leonarde Keeler — WikiTree
Confirms birth in Berkeley, death in Sturgeon Bay, Door County, and family details including parents Charles Keeler and Louise Mapes Bunnell.[3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives.. Named after the polymath Leonardo da Vinci, Keeler preferred to be called "Nard" [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[2]Verified Leonarde Keeler — WikiTree
Confirms birth in Berkeley, death in Sturgeon Bay, Door County, and family details including parents Charles Keeler and Louise Mapes Bunnell.. His mother died in 1907 when he was just four years old, and he and his sisters were raised primarily by their maternal grandparents and attended boarding schools [3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives..

As a teenager, Keeler suffered a serious illness that interrupted his studies [3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives.. During his convalescence, his father — a close friend of Berkeley Police Chief August Vollmer — introduced the young Leonarde to the Berkeley Police Department and to Vollmer's pioneering scientific crime detection methods [3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives.[4]Verified Biography of Leonarde Keeler — American Polygraph Association
Confirms Keeler's birth in California on October 30, 1903, naming after Leonardo da Vinci, teenage illness, and introduction to Vollmer and the Berkeley Police Department.. This encounter ignited a lifelong fascination with deception detection. For more on this pivotal mentor, see our profile of William Marston: The Law Student Who Changed Lie Detection.

While still in high school, Keeler worked for the Berkeley Police Department under Vollmer and became captivated by John Larson's cardio-pneumo psychogram — the rudimentary device capable of detecting deception [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[5]Verified Leonard Keeler — Prabook
Confirms North Berkeley birthplace, Cleveland Torso Murders polygraph of Francis Sweeney, Emotograph fire in 1924, and Call Northside 777 appearance.. Keeler became Larson's keen assistant, gaining firsthand experience in polygraph interrogations [5]Verified Leonard Keeler — Prabook
Confirms North Berkeley birthplace, Cleveland Torso Murders polygraph of Francis Sweeney, Emotograph fire in 1924, and Call Northside 777 appearance.[6]Verified Leonard Keeler — The Father of the Modern Polygraph
Confirms Keeler's 1925 patent, North Berkeley birthplace, ink pen recording innovation, and Associated Research manufacturing details..

University Years and the Emotograph

After graduating from Berkeley High School, Keeler enrolled at the University of California, Berkeley in the fall of 1923 [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[5]Verified Leonard Keeler — Prabook
Confirms North Berkeley birthplace, Cleveland Torso Murders polygraph of Francis Sweeney, Emotograph fire in 1924, and Call Northside 777 appearance.. He soon followed Vollmer to UCLA when the police chief accepted a post as Chief of Police for Los Angeles [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[5]Verified Leonard Keeler — Prabook
Confirms North Berkeley birthplace, Cleveland Torso Murders polygraph of Francis Sweeney, Emotograph fire in 1924, and Call Northside 777 appearance.. Keeler later transferred to Stanford University to study psychology under Professor Walter Miles, where he conducted experiments with early lie detection devices [2]Verified Leonarde Keeler — WikiTree
Confirms birth in Berkeley, death in Sturgeon Bay, Door County, and family details including parents Charles Keeler and Louise Mapes Bunnell.[3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives..

In 1924, Keeler's first handmade polygraph instrument — which he called "the Emotograph" — was destroyed in a fire at his residence [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[7]Verified About Polygraph — History of Lie Detection
Confirms Keeler added the psychogalvanometer (GSR) in 1938, patented prototype of modern polygraph in 1939, and founded Keeler Polygraph Institute in 1948.. Undeterred, he worked with the Western Electro Mechanical Company to build a new instrument that used an ink-based recording system, replacing the cumbersome smoked paper that had plagued earlier devices [6]Verified Leonard Keeler — The Father of the Modern Polygraph
Confirms Keeler's 1925 patent, North Berkeley birthplace, ink pen recording innovation, and Associated Research manufacturing details.[8]Verified A Comprehensive History of the Polygraph — Polygraph UK
Confirms GSR addition in 1938, Keeler Polygraph Institute founding, and validated algorithms exceeding 98% accuracy in real criminal cases.. In 1925, Keeler filed a patent application for his improved device, and the Keeler Polygraph came to market in 1926 as an enhanced version of Larson's original polygraph [6]Verified Leonard Keeler — The Father of the Modern Polygraph
Confirms Keeler's 1925 patent, North Berkeley birthplace, ink pen recording innovation, and Associated Research manufacturing details.[9]Verified About Polygraph — History of Lie Detection (90210 Polygraph)
Confirms Keeler's 1925 ink-pen innovation, 1939 patent as prototype of modern polygraph, and Keeler Polygraph Institute founding in 1948.. Learn about the evolution of this instrument in our Keeler Polygraph Instruments: History & Model Guide.

The Move to Chicago

In 1930, Keeler moved permanently to Chicago to work at the Scientific Crime Detection Laboratory headquartered at Northwestern University [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[2]Verified Leonarde Keeler — WikiTree
Confirms birth in Berkeley, death in Sturgeon Bay, Door County, and family details including parents Charles Keeler and Louise Mapes Bunnell.. He married Katherine (Kay) Applegate, a fellow psychology student, that same year in Chicago [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[2]Verified Leonarde Keeler — WikiTree
Confirms birth in Berkeley, death in Sturgeon Bay, Door County, and family details including parents Charles Keeler and Louise Mapes Bunnell.. Kay became the nation's first female handwriting analyst and later established her own all-woman's detective agency in Chicago specializing in forensic investigation [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts..

The move to Chicago positioned Keeler at the epicenter of American forensic science innovation. The city's combination of high-profile crime, institutional resources, and media attention provided the perfect proving ground for his polygraph ambitions. Keeler's arrival at the SCDL would transform both the laboratory and the entire field of deception detection.

Founding After the St. Valentine's Day Massacre

The Scientific Crime Detection Laboratory (SCDL) was established during the summer of 1929 at Northwestern University, making it America's first independent forensic crime laboratory [10]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms the SCDL was America's first independent forensic crime laboratory, established in 1929, affiliated with Northwestern University, and its educational mission.[11]Verified Teaching Forensic Science — PubMed Abstract
Confirms the SCDL's wide-ranging forensic case work and its founders' ambition to forensically educate police and public.. The lab was founded as a direct outcome of the investigation into the St. Valentine's Day Massacre of February 14, 1929 [10]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms the SCDL was America's first independent forensic crime laboratory, established in 1929, affiliated with Northwestern University, and its educational mission.[12]Verified Scientific Crime Detection Laboratory — Chicagology
Confirms Burt A. Massee as founder/donor, the 1938 sale to Chicago police for $25,000, Fred Inbau's role, and Keeler heading the psychology department.. Burt A. Massee, who had served as foreman of the coroner's jury investigating the massacre, provided the financial backing for the laboratory [12]Verified Scientific Crime Detection Laboratory — Chicagology
Confirms Burt A. Massee as founder/donor, the 1938 sale to Chicago police for $25,000, Fred Inbau's role, and Keeler heading the psychology department.[13]Verified Scientific Crime Detection Laboratory — Northwestern University
Confirms Goddard's role, establishment as country's first independent criminological laboratory, and support from Dean Wigmore..

Colonel Calvin Goddard (1891–1955), a pioneer in forensic ballistics, was appointed managing director and immediately dispatched on an 80-day tour of European police laboratories and medico-legal institutes to find institutional templates for the new enterprise [10]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms the SCDL was America's first independent forensic crime laboratory, established in 1929, affiliated with Northwestern University, and its educational mission.[14]Verified The Birth of the FBI's Technical Laboratory — FBI
Confirms Goddard's lab influenced the FBI, Special Agent Charles Appel received training at the SCDL in 1931, and the Bureau's adoption of scientific crime detection methods.. The SCDL was deliberately established independently of the Chicago Police Department, which was then suspected of corruption and collusion in organized crime [12]Verified Scientific Crime Detection Laboratory — Chicagology
Confirms Burt A. Massee as founder/donor, the 1938 sale to Chicago police for $25,000, Fred Inbau's role, and Keeler heading the psychology department.[14]Verified The Birth of the FBI's Technical Laboratory — FBI
Confirms Goddard's lab influenced the FBI, Special Agent Charles Appel received training at the SCDL in 1931, and the Bureau's adoption of scientific crime detection methods.. With support from Northwestern Law School Dean Emeritus John Henry Wigmore, the laboratory was affiliated with the university's Law School [12]Verified Scientific Crime Detection Laboratory — Chicagology
Confirms Burt A. Massee as founder/donor, the 1938 sale to Chicago police for $25,000, Fred Inbau's role, and Keeler heading the psychology department.[14]Verified The Birth of the FBI's Technical Laboratory — FBI
Confirms Goddard's lab influenced the FBI, Special Agent Charles Appel received training at the SCDL in 1931, and the Bureau's adoption of scientific crime detection methods..

The laboratory undertook a wide range of scientific case work, including toxicology, firearms identification, polygraph testing, the analysis of questioned documents, and bacteriology [10]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms the SCDL was America's first independent forensic crime laboratory, established in 1929, affiliated with Northwestern University, and its educational mission.[11]Verified Teaching Forensic Science — PubMed Abstract
Confirms the SCDL's wide-ranging forensic case work and its founders' ambition to forensically educate police and public.. Its founders envisioned it as a "school for manhunters" and attempted to forensically educate police officers, legal professionals, and the general public [10]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms the SCDL was America's first independent forensic crime laboratory, established in 1929, affiliated with Northwestern University, and its educational mission.[11]Verified Teaching Forensic Science — PubMed Abstract
Confirms the SCDL's wide-ranging forensic case work and its founders' ambition to forensically educate police and public.. For more on the people who shaped this era, see Fred Inbau's Legacy: The Chicago School of Forensic Science.

Keeler's Rise to Laboratory Director

Keeler joined the SCDL in 1930 and quickly became the head of its psychology department, bringing the lie detector "to its present state of perfection," as contemporaries noted [12]Verified Scientific Crime Detection Laboratory — Chicagology
Confirms Burt A. Massee as founder/donor, the 1938 sale to Chicago police for $25,000, Fred Inbau's role, and Keeler heading the psychology department.[15]Verified Fred E. Inbau Papers — Northwestern University Archives
Confirms Inbau became SCDL Director in 1938, Northwestern sold the lab to Chicago PD, and the Crime Detection Lab continued as part of CPD until 1996.. When Calvin Goddard departed Chicago, the laboratory was left in the hands of Fred E. Inbau and a well-trained civilian staff [12]Verified Scientific Crime Detection Laboratory — Chicagology
Confirms Burt A. Massee as founder/donor, the 1938 sale to Chicago police for $25,000, Fred Inbau's role, and Keeler heading the psychology department.[15]Verified Fred E. Inbau Papers — Northwestern University Archives
Confirms Inbau became SCDL Director in 1938, Northwestern sold the lab to Chicago PD, and the Crime Detection Lab continued as part of CPD until 1996.. Keeler ultimately became head of the laboratory in 1936 and held that position until 1938, when he entered private business [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[16]Verified Leonarde Keeler — Geni.com Genealogy
Confirms Keeler moved to Chicago in 1930, became head of lab in 1936, opened first polygraph school, and became first full-time private polygraph consultant..

The SCDL's educative mission proved as significant as its case work. The laboratory offered lectures to Cook County prosecutors, Chicago police detectives, and the broader law enforcement community [10]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms the SCDL was America's first independent forensic crime laboratory, established in 1929, affiliated with Northwestern University, and its educational mission.. It also published the American Journal of Police Science, the first U.S. journal dedicated to forensic science, though the publication was absorbed into the Journal of Criminal Law and Criminology by 1933 due to financial difficulties [10]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms the SCDL was America's first independent forensic crime laboratory, established in 1929, affiliated with Northwestern University, and its educational mission.[14]Verified The Birth of the FBI's Technical Laboratory — FBI
Confirms Goddard's lab influenced the FBI, Special Agent Charles Appel received training at the SCDL in 1931, and the Bureau's adoption of scientific crime detection methods.. As research by Inbau (1985) documents, by 1932 polygraph testing had become the laboratory's primary function, surpassing even ballistics work, with over 2,171 examinations conducted between 1935 and 1938 [17]Verified Scientific Crime Detection: Early Efforts in Chicago
Confirms polygraph testing became the SCDL's primary function by 1932 and documents 2,171 examinations between 1935-1938..

Sale to the Chicago Police Department

By 1938, the Chicago Police Department had lost enough of its gangster-era stigma to purchase the SCDL for $25,000 [12]Verified Scientific Crime Detection Laboratory — Chicagology
Confirms Burt A. Massee as founder/donor, the 1938 sale to Chicago police for $25,000, Fred Inbau's role, and Keeler heading the psychology department.[15]Verified Fred E. Inbau Papers — Northwestern University Archives
Confirms Inbau became SCDL Director in 1938, Northwestern sold the lab to Chicago PD, and the Crime Detection Lab continued as part of CPD until 1996.. The acquisition included two chemical laboratories, a photography room and darkroom, a chamber outfitted with a lie detector, a document examiner's room, a library of approximately 1,000 books on scientific crime detection, and an exhibits room containing hundreds of firearms and other implements of crime [12]Verified Scientific Crime Detection Laboratory — Chicagology
Confirms Burt A. Massee as founder/donor, the 1938 sale to Chicago police for $25,000, Fred Inbau's role, and Keeler heading the psychology department.[15]Verified Fred E. Inbau Papers — Northwestern University Archives
Confirms Inbau became SCDL Director in 1938, Northwestern sold the lab to Chicago PD, and the Crime Detection Lab continued as part of CPD until 1996..

Fred E. Inbau was named Director of the SCDL upon its sale and stayed on as Director until 1941 [15]Verified Fred E. Inbau Papers — Northwestern University Archives
Confirms Inbau became SCDL Director in 1938, Northwestern sold the lab to Chicago PD, and the Crime Detection Lab continued as part of CPD until 1996.[16]Verified Leonarde Keeler — Geni.com Genealogy
Confirms Keeler moved to Chicago in 1930, became head of lab in 1936, opened first polygraph school, and became first full-time private polygraph consultant.. The Crime Detection Lab continued to function as part of the Chicago Police Department until 1996 [16]Verified Leonarde Keeler — Geni.com Genealogy
Confirms Keeler moved to Chicago in 1930, became head of lab in 1936, opened first polygraph school, and became first full-time private polygraph consultant.. The FBI also drew heavily on the SCDL's expertise — Special Agent Charles Appel received training at Goddard's laboratory in 1931 before the FBI Laboratory formally began operations in November 1932 [14]Verified The Birth of the FBI's Technical Laboratory — FBI
Confirms Goddard's lab influenced the FBI, Special Agent Charles Appel received training at the SCDL in 1931, and the Bureau's adoption of scientific crime detection methods..

From Smoked Paper to Ink Pens

The Keeler Polygraph was distinguished by its portability and practical design. In 1925, Keeler devised a polygraph that used inked pens for recording changes in a subject's blood pressure, pulse rate, and respiratory patterns, eliminating the need for smoking paper and preserving it with shellac [6]Verified Leonard Keeler — The Father of the Modern Polygraph
Confirms Keeler's 1925 patent, North Berkeley birthplace, ink pen recording innovation, and Associated Research manufacturing details.[8]Verified A Comprehensive History of the Polygraph — Polygraph UK
Confirms GSR addition in 1938, Keeler Polygraph Institute founding, and validated algorithms exceeding 98% accuracy in real criminal cases.. This seemingly simple innovation was transformative — it made the results immediately readable, permanent, and easy to transport.

The instrument's compact, suitcase-style design allowed examiners to bring the device directly to clients, whether in police stations, corporate offices, or courtrooms. This portability was critical to Keeler's commercial success, as it enabled him to travel nationwide conducting examinations. Explore the engineering details in our guide to the Keeler Polygraph Model 302: The Classic Instrument.

Adding the Galvanic Skin Response

In 1938, Keeler further refined the polygraph by adding a third physiological measuring component — the psychogalvanometer — which measured changes in galvanic skin resistance during questioning [7]Verified About Polygraph — History of Lie Detection
Confirms Keeler added the psychogalvanometer (GSR) in 1938, patented prototype of modern polygraph in 1939, and founded Keeler Polygraph Institute in 1948.[8]Verified A Comprehensive History of the Polygraph — Polygraph UK
Confirms GSR addition in 1938, Keeler Polygraph Institute founding, and validated algorithms exceeding 98% accuracy in real criminal cases.[9]Verified About Polygraph — History of Lie Detection (90210 Polygraph)
Confirms Keeler's 1925 ink-pen innovation, 1939 patent as prototype of modern polygraph, and Keeler Polygraph Institute founding in 1948.. This innovation was based on the earlier work of Fordham University Graduate School psychologist Reverend Walter G. Summers [18]Verified A Review of the Polygraph: History, Methodology and Current Status
Confirms Keeler added GSR in 1938 based on Reverend Walter G. Summers' work, patented his polygraph, founded a polygraph school, and desired commercial success.. The addition of galvanic skin response (GSR) expanded the polygraph's physiological metrics to three channels: respiration, cardiovascular activity, and electrodermal activity [7]Verified About Polygraph — History of Lie Detection
Confirms Keeler added the psychogalvanometer (GSR) in 1938, patented prototype of modern polygraph in 1939, and founded Keeler Polygraph Institute in 1948.[8]Verified A Comprehensive History of the Polygraph — Polygraph UK
Confirms GSR addition in 1938, Keeler Polygraph Institute founding, and validated algorithms exceeding 98% accuracy in real criminal cases..

In 1939, Keeler patented what is now understood as the prototype of the modern polygraph — the Keeler Polygraph [7]Verified About Polygraph — History of Lie Detection
Confirms Keeler added the psychogalvanometer (GSR) in 1938, patented prototype of modern polygraph in 1939, and founded Keeler Polygraph Institute in 1948.[8]Verified A Comprehensive History of the Polygraph — Polygraph UK
Confirms GSR addition in 1938, Keeler Polygraph Institute founding, and validated algorithms exceeding 98% accuracy in real criminal cases.[9]Verified About Polygraph — History of Lie Detection (90210 Polygraph)
Confirms Keeler's 1925 ink-pen innovation, 1939 patent as prototype of modern polygraph, and Keeler Polygraph Institute founding in 1948.. This patent established the template for mass-produced instruments and influenced subsequent designs emphasizing mechanical reliability and ease of calibration. The American Polygraph Association would later recognize Keeler as the "father of the modern polygraph" for these foundational contributions [3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives..

Manufacturing and the C.H. Stoelting Company

The commercialization of polygraph instruments accelerated through partnerships with manufacturing firms. Keeler's instruments were produced by Associated Research, Inc., a Chicago company founded by James F. Inman in 1936 [19]Verified Keeler Polygraph Instruments: History & Model Guide
Confirms Keeler Polygraph models manufactured by Associated Research of Chicago and details of instrument development.. Meanwhile, the C.H. Stoelting Company — originally founded in 1886 as the Chicago Laboratory Supply and Scale Company — created their first Cardio-Pneumo Polygraph in 1935 [20]Verified Our Company — C.H. Stoelting Co.
Confirms Stoelting created their first Cardio-Pneumo Polygraph in 1935, founded in 1886, and has been a pioneer in polygraph instrument manufacturing..

Nearly every major advancement in the field of polygraph instrumentation has come from Stoelting, from electronic recording channels in 1946 to the first computerized polygraph system in 1992 [20]Verified Our Company — C.H. Stoelting Co.
Confirms Stoelting created their first Cardio-Pneumo Polygraph in 1935, founded in 1886, and has been a pioneer in polygraph instrument manufacturing.. For the full story of how polygraph technology evolved into the digital age, see Polygraph Technology: 1990s vs 2020s — How Lie Detectors Evolved and Axciton Systems History: Pioneering Computerized Polygraph.

From Police Work to Corporate America

Keeler became the first full-time private polygraph consultant in America [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[16]Verified Leonarde Keeler — Geni.com Genealogy
Confirms Keeler moved to Chicago in 1930, became head of lab in 1936, opened first polygraph school, and became first full-time private polygraph consultant.. Records made and filed in Keeler's office covered more than 30,000 cases over the course of his career [21]Verified Polygraph — Baltimore Police Museum
Confirms records in Keeler's office covered more than 30,000 cases and documents Keeler Polygraph instrument models.. While these records were never compiled statistically, they demonstrated a high percentage of accuracy and successful results [21]Verified Polygraph — Baltimore Police Museum
Confirms records in Keeler's office covered more than 30,000 cases and documents Keeler Polygraph instrument models..

Keeler's client base extended far beyond law enforcement. Banks, department stores, retail operations, and government agencies all sought his services. By 1935, Keeler had already applied his device to over 4,000 suspects in criminal cases across various departments, contributing to its integration into routine investigations in cities like Chicago and Berkeley [3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives.. His work screening bank employees was featured in a December 1934 radio interview on the Columbia Broadcasting System, where he discussed polygraph applications with legal scholar John Henry Wigmore [3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives..

The 1933 World's Fair Showcase

The Keeler Polygraph gained enormous public visibility when it was featured as a showpiece at the 1933 Chicago World's Fair — the Century of Progress International Exposition [22]Verified The Polygraph Has Been Lying for 80 Years — The Daily Beast
Confirms Cecil Loniello and Tony Grignano were on trial for attempted murder of a police officer, the 1933 World's Fair showcase, and 60% confession rate after polygraph.[23]Verified Will Lie Detectors Ever Get Their Day in Court Again? — Bloomberg
Confirms the February 2, 1935 trial of Grignano and Loniello in Portage, Wisconsin, Judge Clayton F. Van Pelt, and first courtroom use of polygraph.. The World's Fair police exhibit showcased the SCDL's work and demonstrated polygraph testing to millions of visitors. This exposure was instrumental in building public awareness and acceptance of the technology.

The Fair's judge in the 1935 Portage, Wisconsin trial had specifically sought out the polygraph because of the technology's impressive showing at the World's Fair police exhibit [22]Verified The Polygraph Has Been Lying for 80 Years — The Daily Beast
Confirms Cecil Loniello and Tony Grignano were on trial for attempted murder of a police officer, the 1933 World's Fair showcase, and 60% confession rate after polygraph.[23]Verified Will Lie Detectors Ever Get Their Day in Court Again? — Bloomberg
Confirms the February 2, 1935 trial of Grignano and Loniello in Portage, Wisconsin, Judge Clayton F. Van Pelt, and first courtroom use of polygraph.. This connection between public demonstration and courtroom adoption illustrates how Keeler's promotional instincts drove the polygraph's expansion into mainstream acceptance.

The 1935 Portage Trial: First Courtroom Use

On February 2, 1935, Leonarde Keeler administered polygraph examinations in the criminal trial of Tony Grignano and Cecil Loniello in Portage, Wisconsin [22]Verified The Polygraph Has Been Lying for 80 Years — The Daily Beast
Confirms Cecil Loniello and Tony Grignano were on trial for attempted murder of a police officer, the 1933 World's Fair showcase, and 60% confession rate after polygraph.[23]Verified Will Lie Detectors Ever Get Their Day in Court Again? — Bloomberg
Confirms the February 2, 1935 trial of Grignano and Loniello in Portage, Wisconsin, Judge Clayton F. Van Pelt, and first courtroom use of polygraph.[24]Verified February 2, 1935: Polygraph Tests Admissible in Court — History and Headlines
Confirms Leonarde Keeler testified about polygraph evidence in Wisconsin courtroom on February 2, 1935.. The two men stood accused of attempting to murder a sheriff during a robbery, and all evidence was circumstantial [22]Verified The Polygraph Has Been Lying for 80 Years — The Daily Beast
Confirms Cecil Loniello and Tony Grignano were on trial for attempted murder of a police officer, the 1933 World's Fair showcase, and 60% confession rate after polygraph.[23]Verified Will Lie Detectors Ever Get Their Day in Court Again? — Bloomberg
Confirms the February 2, 1935 trial of Grignano and Loniello in Portage, Wisconsin, Judge Clayton F. Van Pelt, and first courtroom use of polygraph.. Judge Clayton F. Van Pelt, who had heard about the SCDL's work, invited Keeler to bring his machine. Both sides agreed to allow the test — the defendants saw little to lose, and the prosecution had only circumstantial evidence [22]Verified The Polygraph Has Been Lying for 80 Years — The Daily Beast
Confirms Cecil Loniello and Tony Grignano were on trial for attempted murder of a police officer, the 1933 World's Fair showcase, and 60% confession rate after polygraph.[23]Verified Will Lie Detectors Ever Get Their Day in Court Again? — Bloomberg
Confirms the February 2, 1935 trial of Grignano and Loniello in Portage, Wisconsin, Judge Clayton F. Van Pelt, and first courtroom use of polygraph..

Keeler strapped his lie detector to each man and determined that both were likely lying [22]Verified The Polygraph Has Been Lying for 80 Years — The Daily Beast
Confirms Cecil Loniello and Tony Grignano were on trial for attempted murder of a police officer, the 1933 World's Fair showcase, and 60% confession rate after polygraph.[23]Verified Will Lie Detectors Ever Get Their Day in Court Again? — Bloomberg
Confirms the February 2, 1935 trial of Grignano and Loniello in Portage, Wisconsin, Judge Clayton F. Van Pelt, and first courtroom use of polygraph.. The polygraph results revealed not only that both men were guilty but also identified each man's specific role in the crime [22]Verified The Polygraph Has Been Lying for 80 Years — The Daily Beast
Confirms Cecil Loniello and Tony Grignano were on trial for attempted murder of a police officer, the 1933 World's Fair showcase, and 60% confession rate after polygraph.. Judge Van Pelt admitted the results as evidence — the first time polygraph findings were used in an American criminal trial. Both defendants were convicted of assault [22]Verified The Polygraph Has Been Lying for 80 Years — The Daily Beast
Confirms Cecil Loniello and Tony Grignano were on trial for attempted murder of a police officer, the 1933 World's Fair showcase, and 60% confession rate after polygraph.[23]Verified Will Lie Detectors Ever Get Their Day in Court Again? — Bloomberg
Confirms the February 2, 1935 trial of Grignano and Loniello in Portage, Wisconsin, Judge Clayton F. Van Pelt, and first courtroom use of polygraph.[24]Verified February 2, 1935: Polygraph Tests Admissible in Court — History and Headlines
Confirms Leonarde Keeler testified about polygraph evidence in Wisconsin courtroom on February 2, 1935..

Outside the courthouse, Keeler declared the conviction "a signal victory for those who believe in scientific crime detection" [22]Verified The Polygraph Has Been Lying for 80 Years — The Daily Beast
Confirms Cecil Loniello and Tony Grignano were on trial for attempted murder of a police officer, the 1933 World's Fair showcase, and 60% confession rate after polygraph.. Yet on the stand, he was measured in his statements, telling the judge he "wouldn't want to convict a man on the grounds of the records alone" [22]Verified The Polygraph Has Been Lying for 80 Years — The Daily Beast
Confirms Cecil Loniello and Tony Grignano were on trial for attempted murder of a police officer, the 1933 World's Fair showcase, and 60% confession rate after polygraph..

The Cleveland Torso Murders

In 1938, Keeler conducted a polygraph test on Dr. Francis Edward Sweeney, the chief suspect in the notorious Cleveland Torso Murders — a series of at least twelve brutal dismemberment killings that terrorized the city between 1935 and 1938 [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[25]Verified Cleveland Torso Murderer — Wikipedia
Confirms Sweeney failed two polygraph tests administered by Leonarde Keeler, who told Ness that Sweeney was the culprit.[26]Verified Solving the Cleveland Torso Murders — Cleveland Magazine
Confirms Keeler brought his machine to Cleveland in secret, administered the test, and told Ness 'That's your man.'. Safety Director Eliot Ness, the famed Prohibition agent who had pursued Al Capone, secretly brought Keeler to Cleveland to examine Sweeney [25]Verified Cleveland Torso Murderer — Wikipedia
Confirms Sweeney failed two polygraph tests administered by Leonarde Keeler, who told Ness that Sweeney was the culprit.[26]Verified Solving the Cleveland Torso Murders — Cleveland Magazine
Confirms Keeler brought his machine to Cleveland in secret, administered the test, and told Ness 'That's your man.'.

Sweeney failed two polygraph tests administered by Keeler [25]Verified Cleveland Torso Murderer — Wikipedia
Confirms Sweeney failed two polygraph tests administered by Leonarde Keeler, who told Ness that Sweeney was the culprit.. According to David Cowles, head of Cleveland's Scientific Identification Bureau who participated in the interrogation, Keeler turned to Ness and declared that Sweeney was the culprit [25]Verified Cleveland Torso Murderer — Wikipedia
Confirms Sweeney failed two polygraph tests administered by Leonarde Keeler, who told Ness that Sweeney was the culprit.[26]Verified Solving the Cleveland Torso Murders — Cleveland Magazine
Confirms Keeler brought his machine to Cleveland in secret, administered the test, and told Ness 'That's your man.'. However, due to lack of additional evidence — and because Sweeney was the first cousin of Congressman Martin L. Sweeney, one of Ness's political opponents — Sweeney was never charged with the killings [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[25]Verified Cleveland Torso Murderer — Wikipedia
Confirms Sweeney failed two polygraph tests administered by Leonarde Keeler, who told Ness that Sweeney was the culprit.[26]Verified Solving the Cleveland Torso Murders — Cleveland Magazine
Confirms Keeler brought his machine to Cleveland in secret, administered the test, and told Ness 'That's your man.'. The case demonstrated the polygraph's investigative value while also highlighting the gap between polygraph findings and prosecutable evidence.

Other High-Profile Cases

One of the earlier uses of the Keeler Polygraph was in 1937, in connection with the murder of five-year-old Roger William Loomis in Lombard, Illinois, where the subject was the child's mother, Grace Yvonne Loomis [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.. Keeler also tested suspects in the high-profile Colorado murder case of college student Theresa Foster in 1948 [27]Verified Keeler, Leonard — Encyclopedia.com
Confirms Keeler began the first polygraph school in 1948, the Cleveland Torso Murders case, the Theresa Foster case, and Call Northside 777 film appearance..

Keeler's role in forensic science was documented in the 1948 film noir docudrama Call Northside 777, starring James Stewart, in which Keeler appeared as himself administering a polygraph test [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[27]Verified Keeler, Leonard — Encyclopedia.com
Confirms Keeler began the first polygraph school in 1948, the Cleveland Torso Murders case, the Theresa Foster case, and Call Northside 777 film appearance.. The movie was based on the true story of Chicago journalists whose articles shed light on the questionable conviction of Joe Majczek for the murder of a police officer in 1932 [27]Verified Keeler, Leonard — Encyclopedia.com
Confirms Keeler began the first polygraph school in 1948, the Cleveland Torso Murders case, the Theresa Foster case, and Call Northside 777 film appearance.. This Hollywood appearance further cemented the polygraph's place in American popular culture.

The Keeler Polygraph Institute

In 1948, Keeler founded the world's first formal polygraph school — the Keeler Polygraph Institute in Chicago [7]Verified About Polygraph — History of Lie Detection
Confirms Keeler added the psychogalvanometer (GSR) in 1938, patented prototype of modern polygraph in 1939, and founded Keeler Polygraph Institute in 1948.[8]Verified A Comprehensive History of the Polygraph — Polygraph UK
Confirms GSR addition in 1938, Keeler Polygraph Institute founding, and validated algorithms exceeding 98% accuracy in real criminal cases.[27]Verified Keeler, Leonard — Encyclopedia.com
Confirms Keeler began the first polygraph school in 1948, the Cleveland Torso Murders case, the Theresa Foster case, and Call Northside 777 film appearance.. The institute instructed students on how to conduct and analyze polygraph examinations, marking the profession's transition from an experimental technique to an established practice requiring specialized education [7]Verified About Polygraph — History of Lie Detection
Confirms Keeler added the psychogalvanometer (GSR) in 1938, patented prototype of modern polygraph in 1939, and founded Keeler Polygraph Institute in 1948.[8]Verified A Comprehensive History of the Polygraph — Polygraph UK
Confirms GSR addition in 1938, Keeler Polygraph Institute founding, and validated algorithms exceeding 98% accuracy in real criminal cases..

The Keeler Polygraph Institute created the professional pipeline that spread the polygraph technique across law enforcement, government, and the private sector. It formalized training standards that had previously been passed down informally from examiner to apprentice. Government agencies increasingly requested Keeler-method training for their personnel, leading to expanded use in federal and local policing [3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives.. If you're interested in pursuing this profession today, explore our guide on how to Become a Polygraph Examiner or browse Polygraph Training opportunities.

The U.S. Army and Federal Expansion

The methods developed at the Keeler Polygraph Institute laid the groundwork for federal adoption of polygraph testing. After Keeler's death, the techniques he pioneered were carried forward by his graduates, who trained examiners across the United States. The professionalization Keeler championed made it possible for standardized polygraph programs to emerge within federal agencies.

The Keeler model 302 polygraph was first introduced to Japan in 1953 and became the pattern for Japanese-produced instruments [28]Verified Polygraph History Holdings — Department of Defense Polygraph Institute
Confirms the Keeler model 302 polygraph was first introduced to Japan in 1953 and became the pattern for Japanese-produced instruments., demonstrating the international reach of Keeler's innovations. For the full story of how polygraph spread worldwide, see our articles on polygraph history in Germany, Soviet Bloc adoption, and Polygraph in the RCMP. The post-war expansion of polygraph testing is detailed in Polygraph in the 1940s: Post-War Boom & OSS Spy Testing.

Keeler's Business Blueprint

Keeler was the first person in the polygraph field to recognize and capitalize on the instrument's commercial potential [18]Verified A Review of the Polygraph: History, Methodology and Current Status
Confirms Keeler added GSR in 1938 based on Reverend Walter G. Summers' work, patented his polygraph, founded a polygraph school, and desired commercial success.. Unlike his mentor John Larson, who viewed the polygraph primarily as a medical and scientific diagnostic tool, Keeler saw its value for law enforcement screening and private sector applications [3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives.[18]Verified A Review of the Polygraph: History, Methodology and Current Status
Confirms Keeler added GSR in 1938 based on Reverend Walter G. Summers' work, patented his polygraph, founded a polygraph school, and desired commercial success.. This commercial vision established the business model that the polygraph profession still follows today.

Keeler's approach was multifaceted: he patented his instruments, built relationships with law enforcement agencies and corporate clients nationwide, promoted the polygraph through media appearances and public demonstrations, and ultimately established a training school to produce qualified examiners. According to unpublished survey data kept in archives, up to 60 percent of the criminals labeled deceptive after an examination with Keeler's polygraph would confess to their crimes [22]Verified The Polygraph Has Been Lying for 80 Years — The Daily Beast
Confirms Cecil Loniello and Tony Grignano were on trial for attempted murder of a police officer, the 1933 World's Fair showcase, and 60% confession rate after polygraph. — a powerful statistic that drove demand for his services.

The Evolution of Polygraph Techniques

Keeler's Relevant/Irrelevant Question technique became the dominant testing methodology during his era [18]Verified A Review of the Polygraph: History, Methodology and Current Status
Confirms Keeler added GSR in 1938 based on Reverend Walter G. Summers' work, patented his polygraph, founded a polygraph school, and desired commercial success.. However, the field continued to evolve after his death. In 1947, John E. Reid, a Chicago lawyer, developed the Control Question Technique (CQT), which incorporated emotionally arousing control questions and replaced Keeler's method as the most widely used technique [8]Verified A Comprehensive History of the Polygraph — Polygraph UK
Confirms GSR addition in 1938, Keeler Polygraph Institute founding, and validated algorithms exceeding 98% accuracy in real criminal cases.[18]Verified A Review of the Polygraph: History, Methodology and Current Status
Confirms Keeler added GSR in 1938 based on Reverend Walter G. Summers' work, patented his polygraph, founded a polygraph school, and desired commercial success..

Modern research has extensively validated CQT-based approaches. A meta-analysis of 14 laboratory studies by Kircher, Horowitz, and Raskin (1988) found that accuracy exceeded 85% across studies [29]Verified Meta-Analysis of Mock Crime Studies of the Control Question Polygraph Technique
Foundational CQT research demonstrating accuracy exceeding 85% across 14 laboratory studies — relevant to the evolution of techniques pioneered in Keeler's era., while foundational mock crime experiments by Rovner, Raskin, and Kircher (1979) established the Federal Zone of Comparison technique validity using numerical scoring [30]Verified Validity of CQT in Laboratory Mock Crime Study
Established Federal Zone of Comparison technique validity using numerical scoring — methods that evolved from Keeler-era foundations.. Cross-validation studies by Raskin, Kircher, Honts, and Horowitz (1988) confirmed the replicability of CQT accuracy across multiple independent experiments [31]Verified Replication and Cross-Validation of Utah Mock Crime Study
Cross-validation study confirming CQT accuracy across multiple experiments — foundational research supporting polygraph techniques evolved from Keeler's work.. The evolution from Keeler's pioneering methods to today's validated scoring approaches, including the Integrated Zone Comparison Technique studied by Gordon and Fleisher (2012) [32]Verified Effectiveness of the IZCT with Various Scoring Systems in a Mock Crime Experiment
Foundational research comparing scoring approaches for the Integrated Zone Comparison Technique — relevant to the evolution of standardized methods Keeler pioneered., demonstrates the enduring impact of the professional infrastructure Keeler built.

For a deeper understanding of how John Reid's 1945 Polygraph Chair advanced the field, and how modern counterintelligence polygraph programs evolved from these foundations, explore our dedicated guides.

Personal Tragedy and Declining Health

Keeler's personal life was marked by tragedy. His wife Katherine left him for another man, Rene Dussaq, and during World War II joined the Women's Auxiliary Service Pilots (WASPs) [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.. She died in 1944 near Patterson Field in Ohio while flying solo across the country to help halt the disbanding of the WASPs [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.. Devastated by her departure and death, Keeler's health deteriorated.

Keeler died on September 20, 1949, in Door County, Wisconsin, at the age of 45, after suffering a stroke brought on by stress, alcohol, and cigarettes [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.[2]Verified Leonarde Keeler — WikiTree
Confirms birth in Berkeley, death in Sturgeon Bay, Door County, and family details including parents Charles Keeler and Louise Mapes Bunnell.[3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives.. He had been visiting the Sturgeon Bay summer home of a fellow criminologist when he suffered the stroke on September 7, 1949, and was taken to Door County Memorial Hospital [2]Verified Leonarde Keeler — WikiTree
Confirms birth in Berkeley, death in Sturgeon Bay, Door County, and family details including parents Charles Keeler and Louise Mapes Bunnell.. His body was returned to Chicago for burial at Graceland Cemetery [2]Verified Leonarde Keeler — WikiTree
Confirms birth in Berkeley, death in Sturgeon Bay, Door County, and family details including parents Charles Keeler and Louise Mapes Bunnell..

An Enduring Professional Legacy

The American Polygraph Association posthumously recognized Keeler as the "father of the modern polygraph" [3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives.. His personal and professional papers, spanning 1899–1972 with the bulk covering 1923–1949, are preserved at UC Berkeley's Bancroft Library, where they remain open for research [3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives.[33]Verified Finding Aid to the Leonarde Keeler Papers — Bancroft Library, UC Berkeley
Confirms Keeler papers (1899-1972) are preserved at the Bancroft Library, his Berkeley birth, Stanford studies, and career at the SCDL..

Keeler's contributions to the polygraph are featured in the documentary film The Lie Detector, which first aired on PBS's American Experience on January 3, 2023 [1]Verified Leonarde Keeler — Wikipedia
Confirms Keeler's birth (October 30, 1903), death (September 20, 1949), Berkeley origins, Northwestern career timeline, marriage to Katherine Applegate, and key biographical facts.. Since his death in 1949, no one in the polygraph field has fully taken Keeler's place — he was simultaneously an inventor, examiner, businessman, instructor, and showman who single-handedly built the infrastructure for an entire profession [3]Verified Leonarde Keeler — Grokipedia
Confirms detailed biographical facts including Berkeley birthplace, GSR addition in 1938, 1939 patent, APA recognition, and Bancroft Library archives..

Learn more about Leonarde Keeler: The Father of the Modern Polygraph Machine in our comprehensive biography. For how his work relates to modern practice, explore our Polygraph Research Database for the latest peer-reviewed studies on polygraph accuracy and methodology.

From Mosso's Plethysmograph to Lombroso's Criminal Testing

Keeler's work did not emerge in a vacuum. The scientific foundations for physiological deception detection were laid by European researchers decades earlier. In 1878, Italian physiologist Angelo Mosso used an instrument called a plethysmograph in his research on emotion and fear, becoming the first scientist to report that breathing patterns change under certain stimuli and that these changes cause variations in blood pressure and pulse rate [34]Verified A Comprehensive History of the Polygraph — Ohio Polygraph Services
Confirms Angelo Mosso used the plethysmograph in 1878 and Cesare Lombroso used the hydrosphygmograph for deception detection in 1895.[35]Verified Brief History of the Polygraph — 90210 Polygraph
Confirms Lombroso modified the hydrosphygmograph in 1895, Benussi's 1914 respiration experiments, and Marston's 1915 blood pressure test..

Building on Mosso's insights, Italian criminologist Cesare Lombroso — often called the father of modern criminology — became the first person to apply scientific instrumentation specifically for determining truthfulness in crime suspects. In 1895, Lombroso modified an existing instrument called a hydrosphygmograph to measure physiological changes in blood pressure and pulse during police interrogations [34]Verified A Comprehensive History of the Polygraph — Ohio Polygraph Services
Confirms Angelo Mosso used the plethysmograph in 1878 and Cesare Lombroso used the hydrosphygmograph for deception detection in 1895.[35]Verified Brief History of the Polygraph — 90210 Polygraph
Confirms Lombroso modified the hydrosphygmograph in 1895, Benussi's 1914 respiration experiments, and Marston's 1915 blood pressure test.[36]Verified From the Archives: Tell Me No Lies — Polygraph History
Confirms Lombroso's use of instrumentation for deception detection in 1895 and Benussi's 1914 respiration experiments.. He also used this device on several occasions in actual criminal cases to assist police in identifying criminals [35]Verified Brief History of the Polygraph — 90210 Polygraph
Confirms Lombroso modified the hydrosphygmograph in 1895, Benussi's 1914 respiration experiments, and Marston's 1915 blood pressure test..

In 1914, Italian psychologist Vittorio Benussi discovered a method for calculating the quotient of inhalation to exhalation time as a means of detecting deception, concluding that lying caused detectable respiratory changes [35]Verified Brief History of the Polygraph — 90210 Polygraph
Confirms Lombroso modified the hydrosphygmograph in 1895, Benussi's 1914 respiration experiments, and Marston's 1915 blood pressure test.[36]Verified From the Archives: Tell Me No Lies — Polygraph History
Confirms Lombroso's use of instrumentation for deception detection in 1895 and Benussi's 1914 respiration experiments.. In 1915, American psychologist William Moulton Marston developed the discontinuous systolic blood pressure test, which later became one component of the modern polygraph [35]Verified Brief History of the Polygraph — 90210 Polygraph
Confirms Lombroso modified the hydrosphygmograph in 1895, Benussi's 1914 respiration experiments, and Marston's 1915 blood pressure test.. These European pioneers established the fundamental principle underlying all subsequent polygraph development: that psychological states produce measurable physiological changes. Keeler's genius lay in transforming this principle from a laboratory curiosity into a practical, portable, commercially viable tool for law enforcement and private industry.

For more on how the polygraph spread internationally, see our articles on polygraph history in Germany and Polygraph Testing in Rwanda.