WARREN — The triggerman in the Pamela Smart murder case – one of the first high-profile trials about a sexual affair between an instructor and a student – has been released from prison after serving nearly 25 years.

William Flynn was 16 and known as “Billy” in 1990 when he and three friends participated in what prosecutors said was Smart’s plot to kill her husband in Derry, New Hampshire.

Flynn pleaded guilty to second-degree murder and served his sentence in Maine.

Scott Fish, a spokesman for the Maine Department of Corrections, confirmed Thursday that Flynn was released. He was granted parole in March on his first attempt, on his 41st birthday.

Flynn got married while behind bars, has a teenage stepdaughter and has earned his GED and electrician’s helper license.

Also released on parole Thursday in New Hampshire was Patrick “Pete” Randall, who restrained Gregg Smart while Flynn shot him in the head.

Pamela Smart, who was 22 when her husband was killed, is serving life in prison without the chance of parole. She admitted to seducing Flynn but said she didn’t plan her husband’s murder.

According to trial testimony, Smart was media coordinator at Winnacunnet High School in Hampton when she first seduced Flynn when he was 15. She told him she needed her husband killed because she feared she would lose everything if they divorced.

The trial was a media circus and inspired the Joyce Maynard novel “To Die For,” which in turn was made into a movie starring Nicole Kidman.