STAMFORD, Conn. (AP) – Robert F. Kennedy Jr. testified Tuesday that he wasn’t always close to his cousin Michael Skakel, but he said he felt obligated to come forward with a man’s claim that implicates other people in the bludgeoning death that sent Skakel to prison.

Skakel’s attorney is asking a judge to allow a jury to hear from the former classmate, Gitano “Tony” Bryant. He wants a new trial for Skakel, convicted in 2002 of the 1975 bludgeoning death of neighbor Martha Moxley in exclusive Greenwich.

Mr. Bryant had said he was with two friends from New York in Greenwich the night that 15-year-old Martha Moxley was killed.

According to court papers, Mr. Bryant has said one friend had met Moxley and “wanted to go caveman on her,” and that the two later told him “We did what we had to do,” and “We got her caveman style.” Bryant made the claim in a 2003 videotaped interview with Skakel’s private investigator. But Mr. Bryant and the other two men have invoked their Fifth Amendment right against self-incrimination.

Skakel Attorney Hubert Santos told the court Tuesday, “It’s our position that if one of the 12 jurors had a reasonable doubt, then we have a different result than we had in 2002.”

Prosecutor Jonathan Benedict said the new evidence is unreliable and may not even be admissible. Mr. Bryant gave a videotaped statement to a private investigator who was never cross-examined, and he later asserted his Fifth Amendment right against self-incrimination when investigators tried to get another statement.

“It is simply not competent evidence,” Mr. Benedict said, adding that a jury would have found it unreliable if it had come up at the 2002 trial. “It is hearsay.”

Mr. Kennedy had put Skakel’s attorneys in touch with Mr. Bryant, the one-time classmate who implicated two friends in the crime.

“I knew that Michael was innocent. I knew he’d been wrongly convicted,” Mr. Kennedy said. “Although my relationship with him was a troubled one, I knew that an innocent man was in prison, and I knew facts that had not been part of the trial and they were not part of the public debate.”

Moxley was bludgeoned to death with a golf club in her wealthy Greenwich neighborhood when she and Skakel were 15. He is serving 20 years to life in prison.

Ethel Kennedy, Skakel’s aunt, sat in the front row of the courtroom.

The hearing is Skakel’s latest bid to overturn his 2002 conviction, and his hair is gray and he appeared thinner than at his trial.

The defense played a tape of a conversation between Robert F. Kennedy Jr. and Mr. Bryant about the two men Mr. Bryant implicated, Adolph Hasbrouck and Burt Tinsley.

“They need to interview and focus on this guy Adolph because he said some very, very, very, very damaging statements that, I mean, just blew me away,” Mr. Bryant told Mr. Kennedy, according to a transcript of the conversation.

Mr. Hasbrouck’s wife has called the claim a lie. Mr. Tinsley has not returned telephone calls seeking comment.

The non-jury hearing could last as long as two weeks. Both sides will be allowed to make opening statements of up to one hour before calling witnesses.

To win a new trial, Skakel’s attorneys must show that Bryant’s account is evidence not available at the time of his trial and that it likely would have changed the verdict.

Dorthy Moxley has said that she still believes Skakel is guilty of killing her daughter.