On the job with the "Lie Detector"

January 22, 2006
By Theresa Schmidt

Are you lying or telling the truth? One person who could figure it out is Skip Chisholm. He's a polygraph examiner for the Calcasieu Sheriff's Department and has been for three decades.  Yet his career is still going strong.

"See the loss of base line here. That's a deception," he says,  explaining the valleys and peaks in a sample test.

Chisholm has seen change as far as cases for which lie detector tests are needed. "When I first started, most of the people I was polygraphing were burglaries and thefts, some homicides, some rapes, armed robberies. But today 60% of my tests are sexual predators, child molestations."

The science has come a long way. Sensors placed on the person being tested help detect changes in blood pressure, breathing and perspiration that help measure deception. Chisholm explains one who lies isn't necessarily the one who did the crime.  "A person could fail a polygraph test and only have information about the crime, and not have committed the crime. And so,  you want to make that determination to tell the detective, 'Look, he's not telling you the truth about this case.' But he may not have actually fired the weapon. He may not have actually robbed the store. He may just have information about it."

And unlike some work more physically demanding, a polygraph examiner can keep going longer than those in some jobs. "I'm too old to be out there chasing criminals on the street and wrestling with them and fighting with them. I don't want to be doing that. I can do this, if I wanted to, 'til I'm 70 or 75, " says Chisholm.

If ever asked to take a polygraph he says it's important to inform the examiner of any medicine you're taking. "It can cause the blood pressure to stay down. It can cause the blood pressure to stay up. It doesn't give a true reading."

Otherwise,  Chisholm says,  if you have to take a polygraph the best advice is relax and tell the truth.

Polygraph tests are not admissible in court, but they help detectives in their investigations.