“Green River Killer” Gary Leon Ridgway’s Polygraph Charts

On Monday, 7 May 1984, polygraph operator Norman R. “Norm” Matzke of the King County, Washington Sheriff’s Office conducted a polygraph “test” of Gary Leon Ridgway regarding the deaths of prostitutes whose bodies had been dumped in or near the Green River beginning in 1982.

Gary Leon Ridgway in 1982

After passing the polygraph, Ridgway, who had been arrested on a prostitution-related charge in 1982, was discounted as a suspect. At the time of Ridway’s polygraph, investigators were primarily focused on an innocent suspect, Melvyn Wayne Foster, who had failed a polygraph “test” administered by Matzke on 20 September 1982.

In 2003, Ridgway, who had been identified as the perpetrator through DNA evidence, was convicted for the murders of 48 women, 42 of whom had disappeared prior to Ridgway’s 1984 polygraph session.

AntiPolygraph.org has obtained copies of Ridgway’s polygraph charts and is making them publicly available for the first time. The first chart is for what polygraph operators call a stimulation or “stim” test. Typically, the examinee is asked to write a number and to deny having selected it as the operator reads off a series of numbers including the number chosen. The operator then tells the subject that he reacted strongly when he denied having written the chosen number. This ploy is intended to convince the subject that the polygraph can read his mind.

Gary Leon Ridgway’s Stim Test

AntiPolygraph.org has not received information regarding the number that Ridgway chose for the stim test.

Next, Ridgway was twice asked a series of nine questions, which are listed below, followed by his answers:

  1. Gary, you have heard all the questions on this test, are there any you are going to lie to? NO
  2. Regarding the deaths of prostitutes, have you told the police the complete truth about that? YES
  3. Is your true last name Ridgway? YES
  4. Have you ever caused the death of a prostitute? NO
  5. Before you were 30 years old, did you ever physically injure anyone without provocation? NO
  6. Were you born in the state of Utah? YES
  7. Do you know of anyone who has killed a prostitute? NO
  8. Before you were 30 years old, did you ever lie about someone to get them into serious trouble? NO
  9. Have you taken any illegal drug or narcotic in the last 48 hours? NO

Questions 1 and 2 appear to be so-called “sacrifice relevant” questions. That is, although they are relevant, they are not scored.

Questions 3 and 6 are irrelevant questions that also are not scored. They serve as “buffers” between sets of relevant and so-called “control” or comparison questions.

Questions 4 and 7 are the relevant questions: they directly concern the matter under investigation.

Questions 5 and 8 are probable-lie “control” questions, to which the subject is secretly expected to lie. Ridgway passed the polygraph because his reactions to these “control” questions were deemed stronger than his reactions to the relevant questions (4 and 7). For more about how polygraph charts are scored, see Chapter 3 of our free book, The Lie Behind the Lie Detector.

It is not clear what purpose question 9, which was not scored, was intended to serve.

The above question list is included in a training document (PDF) prepared by polygraph operator Bob Littlejohn. The document also includes the following notes:

At the time of the polygraph, the subject was a single, 35 year old male. He denied any recent medication or surgery. He denied any nervous disorder or having ever been confined to an Institution. Ridgway denied any “experimentation” with marijuana; speed; LSD; narcotic; or, hallucinogen. He also denied any recent alcohol use.

Ridgway stated his health was, “good”, and denied any history of ulcers; heart condition; emphysema; asthma; tuberculosis; hay fever; breathing problems; diabetes; epilepsy; and, blackouts.

The charts below are from the first and second askings of the above list of questions:

Gary Leon Ridgway’s 1st Polygraph Chart
Gary Leon Ridgway’s 2nd Polygraph Chart

The case of Green River Killer Gary Leon Ridgway is a tragic example of how misplaced faith in the pseudoscience of polygraphy can lead to investigative misdirection, with deadly consequences. A similar case is that of suspected serial killer John Arthur Ackroyd, who in 1977 escaped accountability when a woman he raped failed a police-administered polygraph “test,” while Ackroyd passed one.

For previous discussion of the Ridgway case, see the message board thread, Gary Leon Ridgway, Deadliest Serial Killer in U.S. History, Passed Polygraph and Killed Again.

AntiPolygraph.org sent an e-mail inquiry to polygraph operator Norman R. Matzke seeking comment, but did not receive a reply prior to publication of this article.

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