One of Oklahoma's most notorious murder cases was solved thanks in part to a polygraph test.
The Oklahoma State Bureau of Investigations said the test was crucial in solving the Weleetka murders from 2008.
Overall, polygraph tests are 95% to 98% accurate and investigators use them on a regular basis in criminal cases.
A polygraph test involves sensory pads that record movement, tubes that go around the chest to monitor breathing, finger electrodes that record sweating patterns and devices that record blood volume and blood pressure.
“Some people try biting their tongue, they try doing a lot of things, so we are watching them all the time,” OSBI polygraph examiner Don Faircloth told News 9.
Faircloth said he takes at least an hour to explain the entire process to test takers, then he asks a series of very specific yes or no questions.
“We ask the same questions at least two times, here at the bureau, we nearly always do it three times,” Faircloth added.
In Oklahoma, Faircloth said the judge has the final say as to whether a polygraph test is admissible in court.
It is not allowed very often, but is a very effective investigative tool.
For example, a polygraph test helped link a suspect to the Weleetka murders.
Kevin Sweat is currently awaiting sentencing in the 2008 murders of Skyla Whitaker and Taylor Paschal-Placker of Weleetka, as well as the 2011 murder of his fiancée Ashley Taylor.
While the OSBI was investigating Taylor's murder, Sweat agreed to take a polygraph test.
“Even if they've done the crime, they sometimes will say, ‘Yes I'll take the polygraph,' because they think they can beat it,” Faircloth said.
Sweat's polygraph lead investigators to his father's land, where they found the fiancée's charred remains in a burn pile and .40 caliber shell casings nearby.
The OSBI said those casings later matched the gun used in the Weleetka murders.
“He wasn't really on the radar until we were asked to do a polygraph on him,” Faircloth explained.
Faircloth said the test will never be 100% accurate because of the human factor involved, but it has proven extremely helpful to investigators.
“Because of the information gathered in going to this property, now we've connected the Weleetka case to it,” said Faircloth.
Polygraph tests are also used as a pre-employment tool at several state agencies.
For example, the OSBI, the Oklahoma Highway Patrol and the Oklahoma Bureau of Narcotics give people polygraph tests before hiring them.