The case was tabloid fodder and its legal twists and turns transfixed much of the country. In 1975, a 15-year-old girl was found slain in an affluent Connecticut suburb, bludgeoned to death with a golf club. Michael C. Skakel, a neighbor and a cousin of the Kennedys, was ultimately charged and found guilty of murder, but his conviction was overturned by the state’s highest court.
On Friday, prosecutors announced that Mr. Skakel, 60, would not face a second trial, effectively ending a long fought, notorious case that reached all the way to the Supreme Court.
Proving the guilt of Mr. Skakel, who was convicted in the killing of Martha Moxley in 2002, would be impossible because many of the key witnesses in the case had died, prosecutors said. According to media reports, Mr. Skakel and his lawyer did not comment at Superior Court in Stamford, Conn., where prosecutors announced their decision.
The announcement came exactly 45 years to the day Ms. Moxley was killed in Greenwich, her body discovered under a pine tree on her family’s estate. She had been hit so hard with a golf club that it broke. A piece of the shaft had been used to stab her in the neck.
Mr. Skakel, a nephew of Ethel Kennedy, Robert F. Kennedy’s widow, was 15 and lived in the same gated community as Ms. Moxley. Mr. Skakel answered the door the morning after Ms. Moxley disappeared when her mother, Dorthy Moxley, knocked while searching for her daughter.
The golf club used to kill Ms. Moxley, a steel 6-iron, came from a set that belonged to Mr. Skakel’s mother. But investigators did not find blood, fingerprints or other physical evidence connecting Mr. Skakel to the murder. He claimed that he was watching television at a cousin’s house miles away from the scene of the murder when Ms. Moxley was killed.
Because of the lack of physical evidence it took 25 years for investigators to charge Mr. Skakel. He was found guilty after a three-week trial.
After Mr. Skakel’s conviction in 2002, several jurors said his incriminating words and behavior had convinced them of his guilt. They said that during a taped conversation, he had changed his account of his location during the killing. They also believed that relatives and friends had covered up for him.
The lawyers who appealed Mr. Skakel’s conviction maintained that their client had received poor representation. They said that his lawyer had failed to investigate a witness who could have confirmed that Mr. Skakel was far from the Moxley family’s home at the time of the murder and that his older brother, Thomas Skakel, had probably committed the crime.
The case led to years of investigation, Hollywood treatments and several books. One of them was written by Mr. Skakel’s cousin, Robert F. Kennedy Jr., a former prosecutor and environmental lawyer who provided alternate explanations for the killing and detailed what he charged was a flawed police investigation and prosecutorial misconduct.
“I think Michael is very happy today,” Mr. Kennedy said in a telephone interview on Friday.
Two years ago Connecticut’s highest court, agreeing with Mr. Skakel’s argument, vacated his conviction in a 4-3 ruling, citing shortcomings in his defense.
In the majority opinion, Connecticut Supreme Court Justice Richard N. Palmer wrote that Mr. Skakel’s conviction was founded on a case “devoid of any forensic evidence or eyewitness testimony linking the petitioner to the crime.”
But Justice Carmen E. Espinosa wrote a blistering dissent, pointing to Mr. Skakel’s “financial resources, social standing, ethnicity or connections to a political dynasty,” and the celebrity and notoriety surrounding his case, as possible contributing factors to the court’s decision.
Last year, the United States Supreme Court rejected prosecutors’ attempts to revive the case. The prosecutor’s decision on Friday essentially concludes any attempts to further prosecute Mr. Skakel.
Mr. Kennedy, in Friday’s phone interview, said that “we would have made a mockery of them” if prosecutors had retried the case.
Ms. Moxley’s mother, Dorthy Moxley, said she had spoken with prosecutors and knew that the state would not pursue another trial.
“We’ll never forget Martha, and I would think Michael is very regretful,” Ms. Moxley said.