Michael Skakel (41) has been sentenced to 20 years to life in prison for killing his next-door neighbour when they were both teenagers.
The nephew of Ethel Kennedy, widow of the late Robert F. Kennedy, Skakel, who was convicted in June of murdering 15-year-old Martha Moxley in 1975, wept loudly as he pleaded for leniency before Superior Court Judge John Kavenewsky.
The verdict brings to a close a case that lay unsolved for more than a quarter of a century.
"I'm innocent as charged," he said, crying so hard and so loudly at points during his 10-minute address that his words were difficult to understand.
In handing down the sentence, the judge called Moxley's murder "not only violent but especially vicious." He said: "The last 25 years or so, this defendant has been living a lie about his guilt. This defendant has accepted no responsibility and no remorse to this day".
Moxley's body was found on the lawn of her parents' home in the affluent town of Greenwich, Connecticut, next door to the Skakel home, bludgeoned with a golf club that investigators matched to a set belonging to Skakel's late mother.
The evidence against Skakel, 15 at the time of the murder, was largely circumstantial, with no forensic evidence and no witnesses to the crime.
Skakel was convicted in June after a lengthy battle over whether he should be tried as a juvenile or an adult. A state Supreme Court panel ruled he be tried as an adult, although the judge did use state sentencing law that was in effect in 1975.