A man about to start a second trial for the 2005 samurai sword slaying of his sleeping stepfather, whom he had accused of sexually molesting him, pleaded guilty Monday to manslaughter.

Zachary Gibian, 24, will be sentenced later this month to 25 years in prison, the Suffolk County district attorney's office said.

Gibian had been convicted of nearly beheading Scott Nager, a retired New York Police Department officer, as he slept on a couch at home in Hauppauge, on Long Island, but the state's highest court sided with an appeals court and ordered a new trial. It faulted the trial judge for not allowing testimony about statements made by Gibian's mother.

Gibian, who gave written and videotaped confessions to police just hours after the February 2005 killing, changed his story on the witness stand. He insisted his mother inflicted the fatal blows on Nager, who had an extensive war memorabilia collection, after she discovered her husband sexually abusing him. Prosecutors said there was no evidence of any sexual abuse in the home.

The mother, Laura Nager, maintained her innocence throughout the trial and wasn't charged.

Gibian claimed that numerous times, beginning when he was about 15, Nager would get drunk and force him to perform a sex act on him — sometimes with a pistol against the boy's head. He testified that his mother learned of the abuse the night before the killing, when she walked in on her husband and son in the teen's bedroom.

A key prosecution witness at the monthlong trial was Gibian's friend Troy "T.J." Harrelson, the son of former New York Mets star and manager Bud Harrelson. The younger Harrelson, who recalled few specific details because of his admitted use of marijuana, cocaine and painkillers, said he went to Gibian's home after his friend called him for a ride on the morning of the killing.

Harrelson said when Gibian got in his car, he admitted he had just killed his stepfather and then asked Harrelson to help him dispose of the murder weapon and other items in a trash bin behind a shopping mall.