Former police officer Drew Peterson failed half a polygraph test about his missing fourth wife's disappearance, according to his attorney and the author of a new book.

Peterson, the prime suspect in Stacy Peterson's disappearance, agreed to be interviewed by writer Derek Armstrong and take a lie detector test for the book "Drew Peterson Exposed," Armstrong said.

"He failed half of six questions on the Stacy Peterson polygraph," Armstrong told FOXNews.com. "The questions he failed were directly related to the timeline I had him create."

Peterson's lawyer Joel Brodsky said he doesn't like lie detector tests.

"I don't think they're reliable," he said. "I advised him not to take one." Brodsky said he doesn't know what conclusions, if any, can be drawn from this polygraph.

Peterson got a "deceptive" reading with responses about whether his wife called to say she was leaving him (which he answered "yes" to), whether he knew where she was (he answered "no") and whether he had seen her the night before she vanished (he said "yes").

He got a "not deceptive" reading when he was asked if he physically harmed his wife during the time she disappeared (he said "no"), if he had any involvement in the physical removal of his wife from the home the day she vanished (he replied "no") and whether Stacy Peterson had called him to tell him where the car was parked after she left (he said "yes").

The lie detector test was administered by a well-respected polygraph expert named Lee McCord, according to Armstrong and Brodsky.

Stacy Peterson disappeared suddenly last October. Her body has never been found, and police say they believe she is dead.

Drew Peterson, who is also being investigated in the mysterious bathtub death of his third wife Kathleen Savio, has not been charged in either case. He passed a polygraph he took on Savio.

Armstrong says the ex-cop acted "cold" when he spoke about Stacy Peterson, and he has released some clips of the interview audio tapes to the media in the days since his book hit shelves Oct. 1.

"He became very, very cold. He appeared to be emotionless," Armstrong said. "Frankly, the only time I got him to warm up emotionally was when he talked about himself — and his kids."

In one of the excerpts, Peterson says he worries what will happen to him if his fourth wife turns out to have died.

"She comes up dead or something, they're going to be looking at me," he tells Armstrong. "That's got me a little concerned."

At another point, he says he "spent his days working cons on people" when he was a police officer.

Brodsky said he and Peterson are unhappy about Armstrong's decision to release some of the interview tapes.

"I'm kind of upset about the release of the clips," Brodsky told FOXNews.com. "We kind of look at it as a betrayal. He knows we're disappointed."

As for whether he believes Peterson is guilty, the author is reluctant to say for sure. He said that parts of the interviews with the ex-Bolingbrook, Ill., police officer made him uneasy.

"I don't think there's enough evidence either way, but I'm very uncomfortable," he said. "That's why I'm releasing the tapes."

He admitted he's also making portions of his interviews available for publicity of his book.

Brodsky said he suggested Peterson not speak to Armstrong, but his client wanted to try to "move on with his life" and "get his story told."

"We're not thrilled about it," said the attorney about the end result. "There are some things about that book that are positive. ... He [Drew] has mixed feelings."

Peterson's trial in a gun charges case begins Dec. 8.