STAMFORD, Conn. — A man implicated in the murder that sent Kennedy cousin Michael Skakel to prison said he wasn’t in the exclusive Greenwich neighborhood the night of the crime, according to a recorded phone call involving Robert F. Kennedy Jr. that was played in court yesterday.

Skakel, who is serving 20 years to life in prison, is asking for a new trial in the 1975 bludgeoning death of his neighbor Martha Moxley when both were teenagers.

It wasn’t clear how the taped phone conversation between Mr. Kennedy and Adolph Hasbrouck might affect Skakel’s hopes for a new trial.

Mr. Kennedy testified earlier that although he and Skakel have not always been close, he felt obligated to get involved in the case because he believes Skakel is innocent.

It was Mr. Kennedy who put Skakel’s attorneys in touch with Gitano “Tony” Bryant, a former classmate of Skakel’s who implicated Mr. Hasbrouck and another man, Burt Tinsley, in the crime. Mr. Bryant said he was with the two men in Moxley’s neighborhood the night she was killed.

According to court papers, Mr. Bryant 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.” Mr. 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. Mr. Hasbrouck’s wife has called the claim a lie. Mr. Tinsley has not returned telephone calls.

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

In the tape played yesterday, Mr. Kennedy, who did not know Mr. Hasbrouck, asked, “Were you guys up there on that night, on that night before Halloween?”

“That night we weren’t up there, unfortunately, we weren’t around at that time,” Mr. Hasbrouck replied, according to a transcript of the conversation, in which Mr. Hasbrouck sounded relaxed and laughed with Mr. Kennedy about what they were like as teenagers.

In a different phone conversation, Mr. Bryant told Mr. Kennedy to focus on Mr. Hasbrouck.

“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.

Moxley’s mother, Dorthy Moxley, has said she still believes Skakel is guilty. Ethel Kennedy, Skakel’s aunt and Robert F. Kennedy Jr.’s mother, was also in the courtroom.

“I knew that Michael was innocent. I knew he’d been wrongly convicted,” Robert F. Kennedy Jr. testified. “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.”

Skakel attorney Hubert Santos said jurors should hear Mr. Bryant’s claim, which “shattered what had been a closed case.”

“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,” Mr., Santos said.

Prosecutor Jonathan Benedict said the new evidence is unreliable and may not even be admissible. “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.”

The nonjury hearing could last as long as two weeks.

In November, the U.S. Supreme Court decided not to take up Skakel’s appeal, which claimed a statute of limitations had expired before he was charged.