An official website of the United States government. Here's how you know

##### Official websites use **.gov**

A **.gov** website belongs to an official government organization in the United States.

##### Secure **.gov** websites use HTTPS

A lock () or *https://* means you've safely connected to the **.gov** website. Share sensitive information only on official, secure websites.

Submit SearchSearch

FBI

            -  Most Wanted
            -  News
            -  What We Investigate
            -  How We Can Help You
            -  Submit a Tip
            -  About
            -  Contact Us
            -  Home 
            -  History 
            -  Artifacts 
            -  Facebook Icon 
            -  Email Icon 
            -  Twitter Icon 
            -  Youtube Icon 
            -  Flickr Icon 
            -  LinkedIn Icon 
            -  Instagram Icon 
            -  Search FBISubmit Search 

FBIFederal Bureau of Investigation

# Polygraph Machine Used on Jack Ruby

History

                -  A Brief History 
                -  Directors, Then and Now 
                -  Famous Cases and Criminals 
                -  Field Office Histories 
                -  Wall of Honor 
                -  Artifacts 
                -  Reports & Publications 
                -  Seal & Motto 
                -  Stories & Multimedia 
                -  Timeline 

Polygraph Machine Used on Jack Ruby

This Keeler model 6317 polygraph machine was used on Jack Ruby, the man who shot and killed Lee Harvey Oswald two days after Oswald assassinated President John F. Kennedy. (Click image to view high-res.)

How can the FBI tell whether or not someone is telling us the truth? How can we find the lies? 

One of the ways the FBI verifies information and determines who is a credible witness or source is through a polygraph examination.

The FBI has been employing polygraph examinations in our work since the early days of the FBI Laboratory. Around World War II, the FBI began using polygraphs in the course of investigations to confirm facts and dispel lies. Although we have used polygraphs to screen new employees for many years, since the 2001 Robert Hanssen spy case, we have also been requiring regular polygraph examinations of FBI employees with access to sensitive compartmented information (SCI).

This Keeler model 6317 polygraph machine was used on Jack Ruby, the man who shot and killed Lee Harvey Oswald two days after Oswald assassinated President John F. Kennedy. Mr. Ruby continuously asked for a polygraph test, beginning in December 1963, to prove he was not part of a conspiracy with Oswald.

The polygraph was ultimately granted by the President’s Commission on the Assassination of President Kennedy (also known as the Warren Commission after the chairman, Chief Justice Earl Warren). The examination took place in July 1964.

Interpreting the results of Ruby’s polygraph depends on whether or not Ruby suffered from psychosis. A psychotic subject may not be able to distinguish true answers from false answers and may be convinced he is telling the truth, even though he is not. This, in turn, will not register on the polygraph examination, making it impossible to definitively evaluate the examination.

At the time of Ruby’s polygraph examination, then-FBI Director J. Edgar Hoover commented:

“It should be pointed out that the polygraph, often referred to as 'lie detector' is not in fact such a device. The instrument is designed to record under proper stimuli emotional responses in the form of physiological variations which may indicate and accompany deception. The FBI feels that the polygraph technique is not sufficiently precise to permit absolute judgments of deception or truth without qualifications. The polygraph technique has a number of limitations, one of which relates to the mental fitness and condition of the examinee to be tested.”

----

**Complete list of artifacts﻿**

              -  Most Wanted 
              -  Ten Most Wanted 
              -  Fugitives 
              -  Terrorism 
              -  Kidnappings / Missing Persons 
              -  Seeking Information 
              -  Bank Robbers 
              -  ECAP 
              -  ViCAP 
              FBI Jobs
Submit a Tip
Crime Statistics
History
FOIPA
Scams & Safety
FBI Kids

              -  News 
              -  Stories 
              -  Videos 
              -  Press Releases 
              -  Speeches 
              -  Testimony 
              -  Podcasts and Radio 
              -  Photos 
              -  Español 
              -  Apps 
              -  How We Can Help You 
              -  Law Enforcement 
              -  Victims 
              -  Parents and Caregivers 
              -  Students 
              -  Businesses 
              -  Safety Resources 
              -  Need an FBI Service or More Information? 

              -  What We Investigate 
              -  Terrorism 
              -  Counterintelligence 
              -  Cyber Crime 
              -  Public Corruption 
              -  Civil Rights 
              -  Organized Crime 
              -  White-Collar Crime 
              -  Violent Crime 
              -  WMD 
              -  About 
              -  Mission & Priorities 
              -  Leadership & Structure 
              -  Partnerships 
              -  Community Outreach 
              -  FAQs 

              -  Contact Us 
              -  Field Offices 
              -  FBI Headquarters 
              -  Visit the FBI Experience 
              -  Overseas Offices 
              -  Additional Resources 
              -  Accessibility 
              -  eRulemaking 
              -  Freedom of Information / Privacy Act 
              -  Legal Notices 
              -  Legal Policies & Disclaimers 
              -  Privacy Policy 
              -  USA.gov 
              -  White House 
              -  No FEAR Act 
              -  Equal Opportunity 

# fbi

### federal bureau of investigation

                -   
                -   
                -   
                -   
                -   
                -   

### FBI.gov Contact Center

##### Email updates

          -              -  Accessibility 
            -  eRulemaking 
            -  Freedom of Information / Privacy Act 
            -  Legal Notices 
            -  Legal Policies & Disclaimers 
          -              -  Privacy Policy 
            -  USA.gov 
            -  White House 
            -  No FEAR Act 
            -  Equal Opportunity 

FBI.gov is an official site of the U.S. Department of Justice © 

    - Home
    -  Most Wanted 
    -  News 
    -  What We Investigate 
    -  How We Investigate 
    -  How We Can Help You 
    -  Submit a Tip 
    -  About 
    -  Contact Us 
    - Crime Statistics
    -  Photos 
    -  Video 
    -  Outreach 
    -  History 
    -  FOIA 
    -  Scams & Safety 
    -  FBI Kids 
    - FBI Jobs