Police put ‘a lot of weight’ into a polygraph test

Though the results of a polygraph test aren’t admissible in criminal court, police investigators take the results pretty seriously.

Durham Regional Police Det. Paul Mitton said investigators take those results as gospel, and anyone who passes a polygraph test is usually cleared from an investigation.

“Investigators put a lot of weight into it,” he said.

Mitton described the test, commonly referred to as a lie-detector test, as an investigative tool for police.

Polygraphs are typically given at the tail end of an investigation, he said, when an examination of evidence and interviews has left police with persons of interest but no arrests.

Mitton usually does about 50 polygraph tests a year. He said he schedules 80, but taking a polygraph is a voluntary endeavour, and a lot of people either cancel or don’t show up for their test.

The test measures your pulse, breath, blood pressure and sweat.

When we’re young we’re taught that it’s wrong to lie, cheat, or steal, Mitton explained. When we knowingly do those things as adults our bodies react.

“Your body starts to rebel against that lie,” he said.

A polygraph takes about three hours to complete. It can be a nerve-wracking process for the guilty and innocent, Mitton said.

Mitton said the first 2 1/2 hours are spent talking to subjects, explaining how the equipment works and what he’s looking for, all the while stressing that the test is voluntary.

There are also no surprise questions. Mitton said subjects know what they’re going to be asked before they’re hooked up to the machine, which is actually a computer with specialized software.

Tests are usually followed by an interrogation, conducted by Mitton.

Mitton can’t testify in court about a polygraph’s results. But he can tell the court about that interrogation.

Some people confess to crimes after they’re confronted with a deception, he said. Some walk out with Mitton when confronted with the test results.

“In that case I just have to follow them down the hall and make sure they go out the right door,” Mitton said.

Failing a test, he said, is not grounds to make an arrest.

City police Insp. Larry Charmley said the service uses polygraph testing about a dozen times per year. City police don’t have a polygraph machine. Charmley said they either work with Durham police or the OPP when it’s required.