Can lie detectors really tell the truth?

When confessed serial killer Robert Lee Yates Jr. passed a lie-detector test in an attempt to prove he wasn't hiding bodies from investigators, it put the spotlight on a technology that hasn't changed much in decades.

Polygraph tests measure perspiration, blood pressure and heart rate to determine whether a person is answering yes-or-no questions deceptively.

Polygraphs have been used in other high-profile criminal investigations: the killing of a homeless man in Seattle by three teens, the rape allegations against Husky football player Jerramy Stevens and the case against serial killer Ted Bundy.

But lie-detector results are not allowed in court, unless the judge and both sides agree to admit them. That has effectively banned polygraph tests from trials.

The issue is reliability.

Seattle defense attorney John Henry Browne said he stopped believing in polygraph tests after Bundy, his one-time client, passed one.

Shelton Musgrave passed a lie-detector test affirming he never touched a homeless man who was beaten and stabbed near Green Lake last year. But a forensic scientist discovered blood spatters on Musgrave's boots, and a jury convicted him of first-degree murder in July.

Defense attorneys and police say polygraphs are helpful in some situations, but there are no consistent policies regarding their use.

For example, King County sheriff's deputies routinely use lie-detector tests, but King County prosecutors don't ask for the test and don't consider polygraph results presented by defense attorneys before trial.

First used in police interrogations in 1924, lie detectors essentially measure the physical signs of stress. Before administering the test, the examiner tells the subject what questions are going to be asked and asks if the subject understands them.

A polygraph has three components: a cuff that measures blood pressure, a metal thimble that detects perspiration and two convoluted rubber tubes that are placed over the subject's chest to record respiration. The examiner often asks three sets of identical yes-or-no questions. Each set includes six irrelevant questions and three questions pertaining to the crime. The examiner then determines whether the answers were deceptive, not deceptive or inconclusive.

The state has no licensing or training requirements for people who administer lie-detector tests.

The polygraph examiner for the King County Sheriff's Office, Norm Matzke, says the tests aren't always accurate but most people can't trick the machines. When a polygraph gives false readings, it's often because the person conducting the test misinterpreted the results or asked poor questions, he said.

"There's nothing that's 100 percent fail-safe, but it's not the instrument. It's the examiner," Matzke said. "How are you going to control how much you perspire, your heart rate, your blood pressure?"

Matzke has administered lie-detector tests for 29 years but has testified about the results only a few times. More often, he goes to court to tell a jury about a confession given after a defendant failed a polygraph test.

Some prosecutors call for the test to reassure them a defendant is telling the truth in a plea bargain, even though the results won't be presented to a jury.

That was the case with Yates. The polygraph indicated that Yates' statements about his victims were not deceptive, affirming to Spokane County Prosecutor Steve Tucker that Yates was acting in good faith.

The conclusions of the Yates polygraph test have since been disputed by several consulting examiners, who said the results were inconclusive.

Seattle attorney Michael Hunsinger said he uses polygraph tests to determine whether he wants to represent someone charged with a crime.

"It's basically a screening tool for me," he said. "If I have a client who is telling me something that is significantly different from the allegation, it's a way for me to determine the truth. I don't represent guilty people."

Hunsinger recently represented Stevens, the Husky football player who steadfastly claimed he was not guilty of raping a UW student after a June fraternity party.

In August, Stevens passed a lie-detector test. Hunsinger said he told prosecutors of the results, but they weren't impressed. No charges were filed against Stevens, however, after prosecutors determined they could not prove the charge beyond a reasonable doubt.

"The short answer is: We don't use them (polygraphs)," said Mark Larson, chief criminal deputy at the King County Prosecutor's Office. "It's not hocus-pocus; it's like predicting the weather. The courts have decreed a high standard, and there's a reason for that."

King County detectives, on the other hand, often test suspects and witnesses. The case against Leonard Underwood is an example.

On July 2, a motorist discovered the body of James Heard on an embankment three miles east of Enumclaw along Highway 410.

Heard's roommate Doris Butler told detectives she and Heard went to buy crack cocaine from Underwood at his Tacoma home, but she said she didn't know what happened to Heard.

On July 4, Butler agreed to take a polygraph. As she waited for the examiner to arrive, Butler broke down and said Underwood shot Heard over a $10 piece of rock cocaine, according to court papers.

Police arrested Underwood and his cousin, Calvin Myers. In court papers, detectives noted Myers failed a polygraph test and showed "extreme deception" when asked if he saw the homicide and helped dispose of the body. Underwood is to go on trial for second-degree murder in January.