How do lie detectors actually work?

West Virginia

KANAWHA COUNTY, W.Va. (WOWK) – We all have a favorite crime drama that lets us tap into our inner detective. What questions would you ask to break a suspect? And, how would you do it? A seasoned investigator sat down with WOWK 13 News to show how he gets inside the criminal mind.

Now retired, Sean Crosier has been on the real-life side of crime-fighting for almost 30 years, rising to the rank of captain with the Kanawha County Sheriffs Department.

“I administered about 2,000 polygraphs while I was there,” stated Crosier.

And the polygraph is the one tool he still uses today, conducting polygraphs through court-ordered “post convicted, sex offender testing” which helps with therapy and treatment.

“We’re in the victim prevention business as well,” Crosier said. “Each offender is tested every six months to see if they are doing anything they shouldn’t be doing, or if they’ve re-offended.”

Whether being used in treatment or in cracking a criminal case, how exactly do lie detector tests work?

“Basically, what we’re doing is recording the physiology as it relates to the psychology going on in someone’s mind,” Crosier added.

Crosier uses a frequently calibrated medical-grade piece of equipment. Pricing in at about $10,000, it measures among other things, blood pressure, pulse, respiration, and skin perspiration.

Crosier says people come up with a variety of ways to beat the machine-like putting a tack in their shoe or pinching themselves. However, they don’t actually work. Those actions will show up as a huge rise in blood pressure and it becomes a red flag.

“You can alter the data but you cannot beat the polygraph or cause deception to look like truth,” said Crosier.

But, there is a small percentage of the population, less than one percent, who themselves are wired mentally to beat the machine.

“People who have split personalities, if they are in personality A when committing a crime and personality B when taking the test because there would be no memory,” said Crosier. “Anything less than that, I don’t think so.“

Another tool Crosier swears by is kinesiology, or learning to read body language.

“As he started explaining to me what he saw, he went like this (shows gun motion with hand),” stated Crosier. “That to me is a gun. That to him is a gun. I was able to get the confession out of him by using kinesiology. He was exhibiting not only in the polygraph but in his body language afterward. We went in thinking he was the witness but he ended up being the murderer.”

In West Virginia, Crosier says these tests are not admissible in court. However, he believes they are very reliable tools for investigation.

Copyright 2019 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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