Prosecutors would not comment yesterday. But their willingness to grant immunity to the man, Kenneth Littleton, who was living next door to the teen-ager, Martha Moxley, when she was killed in 1975, appears to narrow the case significantly, with the focus now falling on Thomas and Michael Skakel, nephews of Robert F. Kennedy.
Mr. Littleton testified before the grand jury in Bridgeport for about an hour and a half, said his lawyer, Eugene J. Riccio. He refused to discuss the nature of the testimony.
John W. Moxley, 39, Ms. Moxley's brother, who has pushed for further investigation into his sister's killing, said today that he was both surprised and hopeful to hear that Mr. Littleton, who had lived in the Skakel home as a tutor, had testified.
''Ken was there,'' said Mr. Moxley, who now lives in New Jersey. ''He was at ground zero. He was in the Skakel house that night and during the immediate period afterward. He knew what they were talking about. He knew who was in the house. He had a sense of where people were and what they were doing.''
The news that Mr. Littleton had testified, Mr. Moxley said, ''kind of raised the hair on the back of my neck.''
Ms. Moxley, 15, was killed on Oct. 30, 1975, after spending the evening next door at the Skakel house in the gated community of Belle Haven. When she was found under a tree near her house, her underpants had been pulled down, but law enforcement officials have said there was no obvious evidence of sexual assault.
At the time, Thomas Skakel, who was 17, told police that he last saw her alive outside his home about 9:30 P.M. She is believed to have been killed about 10 P.M., beaten with a golf club with such force that the club shattered, and then stabbed through the neck with one of the pieces.
Thomas Skakel now lives in Massachusetts with his wife and their three children. Michael Skakel, who was 15 when Ms. Moxley was killed, is also married and lives in Cohasset, Mass. In 1994 he began working as a driver for his cousin Michael Kennedy.
The golf club had belonged to Ann Reynolds Skakel, the wife of Rushton W. Skakel, Ethel Kennedy's brother and the father of the Skakel boys.
Thomas and Michael Skakel have denied involvement in the murder. Emanuel Margolis, a lawyer for Thomas Skakel, could not be reached late this evening. The case received renewed attention with the publication of Mark Fuhrman's book ''Murder in Greenwich: Who Killed Martha Moxley?'' in April. Mr. Fuhrman, a former Los Angeles police detective, achieved notoriety after testifying in the O.J. Simpson murder trial, and then wrote a book based on his experiences, ''Murder in Brentwood.''
Mr. Littleton, who now lives in Massachusetts, initially refused to testify before the grand jury, invoking his Fifth Amendment right against self-incrimination, Mr. Riccio said. Today, after negotiations with Mr. Littleton, State's Attorney Jonathan C. Benedict asked Superior Court Judge John J. Ronan to compel Mr. Littleton to testify, Mr. Riccio said. The move under state law gives him immunity from prosecution for any crime except perjury in this case.
Although Mr. Riccio would not discuss what Mr. Littleton said today, he did say of his client, ''He's much relieved, and he would like to put this situation far, far behind him.''
Mr. Moxley said the prosecutor's decision to give Mr. Littleton immunity indicates that he believes that Mr. Littleton did not commit the crime.
''I'm assuming that if the police are willing to grant immunity, they knew something we don't know,'' he said.
Grand juries are unusual in Connecticut; fewer than a dozen have been convened since 1985, when the state limited its grand jury proceedings. This one consists of one person, George N. Thim, a former Bridgeport judge who was appointed in June. He will decide whether there is enough evidence for an indictment.
''We've never gotten this far before,'' Mr. Moxley said. ''We're cautiously optimistic.''
(NEW YORK TIMES)