Polygraphs still rare but helpful to investigators, MBI says

Published 11:29 am Thursday, July 12, 2012

Though not completely foolproof, polygraph tests can round out an investigation when clues are few, said the state’s top investigator.

“You get a really, really in-depth interview,” said Lt. Col. Larry Waggoner, director of the Mississippi Bureau of Investigation, during an address Wednesday to the Vicksburg Lions Club. “We may be picking up information we didn’t have prior to it. They may not confess, but you still pick up a lot of good information.”

Modern-day computerized polygraphs that test physiological changes in the body when questions are asked have replaced the old analog, “chart, ink and pen” museum pieces of decades ago, Waggoner said. Still, the practice has been limited to law enforcement since the Employee Polygraph Protection Act of 1988 prohibited most private employers from using polygraphy on current or prospective workers. It exempts government agencies or industries tied to security.

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Algorithms are created by computers to express how blood pressure, breathing patterns or other cardiovascular changes might be related to a subject’s answers, Waggoner said. Technology, though, may not become capable of producing an error-free tool for investigators.

“It’s about 85 percent accurate,” Waggoner said. “There’s been a lot of changes with it through the years, but is it ever going to be 100 percent? Never. I don’t think it will be. There’s too many variables.”

The U.S. Supreme Court has left it up to individual jurisdictions whether the test’s results are admissible in court, ruling in 1998 that no consensus existed on the practice’s reliability.

Psychologists have agreed it is a useful investigatory tool, but isn’t scientifically sound and can produce failing grades for people later determined to be innocent.

However, the tests are used routinely on sex offenders after they exit jail. In Mississippi, lie detector results generally are not admitted into evidence. “Both sides — the prosecutor and the defense — have to agree to it, and that’s not going to happen,” Waggoner said.

About 35 polygraph examiners are licensed through the Mississippi Board of Polygraph Examiners, Waggoner said. Examiners take classes for about 11 weeks to become accredited, he said.