The Connecticut Supreme Court unanimously upheld Kennedy cousin Michael Skakel's murder conviction Friday, more than 30 years after a killing that sparked decades of intrigue.

Skakel, a nephew of Ethel Kennedy, was convicted in 2002 of bludgeoning his neighbor, Martha Moxley, to death with a golf club in 1975 in wealthy Greenwich. Skakel, who along with the victim was 15 at the time, is serving 20 years to life in prison.

He appealed his conviction to the Connecticut Supreme Court last year, arguing among other things that the statute of limitations had expired when he was charged in 2000.

"We're of course very pleased," said Bridgeport State's Attorney Jonathan Benedict. "We felt it was a very clean trial. It's just a great relief to have this behind us."

Dorthy Moxley, Martha's mother, told The Associated Press on Thursday that she was told by prosecutors that the high court had rejected Skakel's appeal.

"I'm not at all doubtful Michael did this. I know he did this," Moxley said. "I hope this is the last we'll hear of them."

Michael Sherman, Skakel's trial lawyer, said he was surprised by the decision.

"Nothing will ever change my opinion that an innocent man is in jail," he said. "He's simply not guilty."

Defense attorneys had argued that, at the time of the killing, the statute of limitations was only five years so Skakel could not be prosecuted.

Skakel still has a petition for a new trial pending in Stamford Superior Court. In that appeal, the cousin of basketball star Kobe Bryant implicates two other men in the murder. Prosecutors have said they are skeptical of that claim.