PERRYVILLE — Polygraph tests have long helped police agencies determine if suspects are telling the truth. But Perry County, Mo., detective Brian McCain is convinced voice analysis is even more accurate.
McCain is a certified user of a Computer Voice Stress Analyzer — a truth verification device. The Southeast Missourian reports that the Perry County department has used the voice stress analyzer more than 100 times since purchasing it six years ago.
The department is among 151 agencies in Missouri using the equipment. Only California and Ohio have more agencies using the device.
The National Institute for Truth Verification developed the CVSA and was introduced to law enforcement in 1988. Perry County authorities have used it for six years.
McCain admits he was skeptical after using polygraph testing for much of his career. Not anymore.
"It's 100 percent, there (are) no inconclusives with a CVSA," he said.
Sheriff Gary Schaaf began using the CVSA because of its accuracy and cost, which is less than polygraph equipment. Schaaf said the equipment has helped clear suspects and garner confessions in various types of crimes.
"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."
A microphone plugs into a computer to analyze a person's response to a question. Unlike a polygraph, it isn't limited to yes-and-no answers and can be used over the phone or with audio recordings, Schaaf said.
The CVSA, in a graph on the computer screen, displays changes in a person's voice frequency. When a person is lying, the involuntary nervous system causes an inaudible peak in their voice, which is displayed on a graph.
Schaaf said: "There are certain muscles in your throat that are connected to the autonomous nervous system. 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.
He said a change in voice frequency is something a person has no control over.
Perry County authorities were recently investigating a burglary at a business in Perryville. McCain performed seven CVSA tests in a week to narrow the field of suspects from seven to one.
The website for the National Institute for Truth Verification said the 2007 murder of a 9-year-old girl in southwest Missouri was solved after two suspects took a CVSA test. Polygraph tests in the case were inconclusive, but the CVSA test determined both men were deceptive.