Perry County sheriff uses Computer Voice Stress Analyzer to eliminate suspects, get confessions

Monday, August 23, 2010
Perry County Sheriff Gary Schaaf explains how to read the results of the Computer Voice Stress Analyzer that the department uses to verify truthfulness when questioning people about cases. (Kristin Eberts)

PERRYVILLE, Mo. -- When Perry County detective Brian McCain was sent four years ago to become a certified user of a Computer Voice Stress Analyzer -- a truth verification device -- he was skeptical.

After using polygraph testing for much of his career, the CVSA, developed by the National Institute for Truth Verification, seemed too simple, McCain remembers thinking.

"By the end of the class, [the instructor] made a believer out of me," McCain said. "It's 100 percent, there [are] no inconclusives with a CVSA."

The Perry County Sheriff's Department began using the voice stress analyzer more than six years ago, when Sheriff Gary Schaaf was looking for truth verification equipment that was cost-effective and time-efficient.

Polygraph testing, Schaaf said, was too expensive and he and his deputies could spend too much time away from the office training to use the equipment.

Since purchasing the CVSA, Schaaf and McCain have used the device more than 100 times. They've used it to clear suspects and to garner confessions in various types of crimes.

Perry County is one of 151 law enforcement agencies in Missouri using the CVSA. Missouri ranks as the third largest user in the U.S. Only California and Ohio have more agencies using the device, which was introduced into the law enforcement community in 1988.

"Basically, what it works off of is your mind and your mouth have to say the same thing," McCain said. "If your mind says yes and your mouth says no, you're caught."

The CVSA uses a microphone that plugs into a computer to analyze a person's response. It's not limited to 'yes' or 'no' answers and can be used over the phone or with audio recordings, Schaaf said.

In a graph on the computer screen, the CVSA measures and displays changes in a person's voice frequency. When a person is lying, their involuntary nervous system causes an inaudible peak in their voice, which is displayed on a graph.

"There are certain muscles in your throat that are connected to the autonomous nervous system," Schaaf said. "When you're telling us the truth it won't be constricted and we'll get a good high chart. When you know you're telling us something that's not true, it constricts your muscles. ... Then we get the blocking chart."

Changes in voice frequency, Schaaf added, is something a person has no control over.

Most recently, McCain said he used the CVSA to determine a prime suspect in a business burglary in Perryville. He performed seven tests just last week, he said, narrowing the field of suspects from seven to one.

"All of my attention can now be focused on the one person," McCain said. "It's a very useful tool, but it's only as good as the person behind the monitor. If you don't ask the right questions, then obviously you don't get the right results."

Schaaf recalled using the CVSA in a 2006 theft investigation. Someone had stolen chainsaws and firearms from a person's shed on Route O in Perry County. Their prime suspect agreed to take a CVSA test.

Schaaf asked the man a series of questions, including whether he bought the missing gun and the chainsaws.

The man didn't pass the CVSA, ended up confessing and even led officers to where he buried the stolen items.

"We would have never found those things; they were buried under a brush pile in a sinkhole," Schaaf said. "We use these things to verify [a suspect[']s] story, and the story he was giving us, obviously, cannot be verified because he wasn't telling the truth."

According to the NITV website, the 2007 murder of a 9-year-old girl in Southwest Missouri was solved after two suspects, David Speares and Chris Collings, took a CVSA test. Polygraph tests the pair took before police discovered the girl's body were determined inconclusive by the FBI, while the CVSA test determined both men were deceptive. They both were interrogated by the Neosho Police Department, confessed and led detectives to the body.

In Cape Girardeau County, Jackson Police Department chief James Humphreys remembers using the tool as a detective years ago. Using the CVSA was much quicker than using a polygraph test -- his usual truth verification tool of choice.

"I really remember it being helpful as far as eliminating a couple different individuals," he said. "It helped lead me in the right direction at the time."

Cape Girardeau County Sheriff John Jordan said his department uses a polygraph and haven't used a CVSA.

Bollinger County Sheriff Leo McElrath said he hasn't used the CVSA yet though it's been offered by Schaaf.

"I intend to," McElrath said. "I'm looking forward to finding an opportunity to use it."

In Scott County, investigator Branden Caid has been certified to use a CVSA test since 2008. The Scott County Sheriff's Department uses the device to interview potential suspects several times a month, also for various instances of criminal activity.

"I've used it for misdemeanor thefts, sex cases, and we've used it in the Angela Mischelle Lawless case," said Caid, who's also a charter member of NITV. "It has a lot less limitations than a polygraph."


Pertinent Address:

710 S. Kingshighway St., Perryville, MO.

Map of pertinent addresses

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