Polygraphs controversial, but serve as investigative tool - KWWL - Eastern Iowa Breaking News, Weather, Closings

Polygraphs controversial, but serve as investigative tool


"We want the person to pass. We don't want them to fail," says polygraph examiner, Rob Duncan, a Waterloo Police Investigator and FBI-trained polygraph examiner.

Investigator Duncan recently gave KWWL a polygraph demonstration, as he attached numograph sensors to his lie-detector subject for the demonstration, Waterloo Police Investigator, Jason Choppard. The numographs monitored Jason's breathing patterns during questioning.

Duncan says, "Some people breathe a little bit differently, so, it's watching both, like a chest breather and an abdominal breather, and a polygraph is just something to get to the truth."

While generally not admissible in Iowa courts, the test results can certainly help investigators eliminate possible suspects.

"If they pass, great. They've passed the test. There shouldn't be any problem with this person. If they fail it, then we ask them, you know, Why did you fail. What were you thinking about when you were taking the test? And, every once in a while, we come across somebody who's like, 'Hey, you know, I failed because I did it.' When that happens, the admission is admissible in court."

For the polygraph demonstration, Duncan asks, "Jason, have you ever lied to any supervisor here at the Waterloo Police Department?"

Jason answered by asking a question himself.  "Lied, he says. No."  Rob reminds him, "Just answer Yes or No, okay?"

That's because all questions are to be answered Yes or No. Subjects are to give no explanation whatsoever; just a Yes or No answer.

Polygraphs begin with several general questions—known as the base questions or irrelevant questions. Later, the examiner asks what are called the Bait or Control questions; these are the questions truly relevant to the investigation.

"If they're lying, or when they're lying, their body is going to react to it. So, basically, all a polygraph does, is it gives a reading, via all the instruments that are hooked up to them. They say No, and they're lying. Typically, the body is going to react to that."

But, there's is no formula in determining if a subject is telling the truth. The results are the interpretation of the Polygraph examiner.

Polygraph exams have long been controversial. Critics of polygraphs say the test is inherently biased against innocent individuals.

But, While the polygraph exam is generally not admissible in court, it can be a value investigative tool for officers.


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