admin @ Sun, 2006-09-17 11:00
For more than 30 years, McCann has seen thousands sweat it out while wired up to a polygraph machine monitoring what the early 1980s rock band the Police put to lyrics: "Every breath you take, Every move you make ... I'll be watching you."
Rubber tubes wrapped around your chest and belly monitor breathing, your heart rate and blood pressure is recorded with a cuff, and something called electro-dermal activity - more or less your sweatiness - is registered by placing two small attachments to the fingers or palm of the hand.
A polygraph combines a few simple medical devices to monitor the body. As a person is questioned, the examiner looks for physiological changes, or lack thereof, to determine what's true and what's deception.
While admitting a small percentage of the general population is unreadable, whether because of obesity or other physiological reasons, accuracy is generally accepted to be 90 to 95 percent, if not greater, depending on the study, he says.
Information gained from polygraph results and the interviews can often point an investigator in the right direction; it can eliminate a subject as a suspect or help show a suspect has nothing to hide. And some employers, mostly government-related, use the polygraph as a screening tool.
"Blood pressure rises or you get a change in heart rate in combination with a galvanic (sweat) response," said McCann, describing a fairly common pattern associated with deception. "With respiration, there's a lot of different responses - some might stop breathing for 5 or 10 seconds, suppress it in some way or it may speed up."
McCann comes from a family with a long history of law enforcement. His father, grandfather, uncle and other relatives worked for the Chicago Police Department, his grandfather in the crime lab throughout the 1930s.
Working his way through college as a bank teller, McCann found his calling. It was during this time that money came up missing and the bank had its tellers submit to a polygraph.
"One-third were suspended, and four to five were fired," McCann said in astonishment, noting he was not among that group of employees. "It wasn't the results, it was what they admitted to doing that amazed me."
That amazement led McCann to enroll in Reid College - to become a polygraph examiner - after graduating from DePaul University. In 1976, he got his state-issued license, and for the next four years worked in the private sector. He later took a job with the State Police in 1980.
Now 53, McCann, who is one of only nine state police polygraph examiners in Illinois, said the types of criminal cases coming through his door have changed, from mostly vandalism, theft and burglary to battery and sex-related crimes. He often performs two polygraph examinations per day, nearly every day of the week.
Since 1921, when William Marston was credited with developing the first modern polygraph, not a great deal has changed. While the testing devices were pulled together into one instrument, the same four physiological patterns continue to be examined. Equally as important as the development of the technology was the development of the type of questions to be asked.
Other patterns such as pupillary reactions and gastro-intestinal changes have been studied, but including them has not been shown to increase accuracy.
The polygraph has transformed. From a mechanical instrument - using paper and ink to record changes - to an electronic device, also using paper and ink. In the early 1990s, many turned to computers and digital recording.
Another big change, in the way of use, came in 1988 with the federal Polygraph Protection Act prohibiting employers from using polygraph for employment screening. The act excludes government and police, which still use the practice.
"That's the biggest response - that it looks like an electric chair," McCann says of the utilitarian "hot" seat complete with wooden arms and metal frame where those being questioned are monitored.
The walls inside are stark white, no decoration. A desk, a few boxes, another chair and a tiny, darkened window where a hidden camera sits. On the desk sits a laptop, a printer, and of course a small network of wires.
Take to the Internet, and you'll find dozens of Web sites advertising how to beat a polygraph. Some sell instruction videos by licensed examiners.
"I wouldn't say it's impossible, and I'm sure there are people who have, but it's very rare," McCann says. "What you'll find on the Internet is a 'how to,' but what you won't get is the experience."
Not only would a person have to "train" their bodies to not show the kind of physiological responses examiners look for, but also a person would have to know how to create a different kind of response.
"Put a tack in their shoe, flex their arm, curl toes, bite the tongue - it won't work," McCann said. "I tell people a tack in your shoe is only going to give you a sore foot."
"You won't ever see a person strapped to a chair with 10 investigators firing away with questions - that's the Hollywood version," he said, noting the real life situation is not quite as exciting or intense. There are only two people in the room: the examiner asking questions and the person answering.
"Most people are surprised how long it takes, and amazed at some of the questions," McCann said. "And no, it's not like 'Meet the Parents.' "
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