The U.S. Supreme Court said Monday that it will not hear the case of Kennedy cousin Michael Skakel, marking the latest twist in a murder case that dates back decades.

The move by the high court to decline the state’s request to take up the case leaves in place a decision that vacated the murder conviction against Skakel.

But it may not be the end of the case. State's Attorney Richard Colangelo tells News 12 that even after the high court's decision, he plans to continue to pursue the case and says he will go over the police reports again.

Michael Skakel was convicted in 2002 after decades of investigations into the 1975 bludgeoning death of his Greenwich neighbor, Martha Moxley. Her body, beaten with a golf club, was found in her family's backyard. Skakel and Moxley were 15 when she was killed.

Skakel was in prison for 11 years. A 2018 decision by the state’s highest court threw out Skakel's conviction. Connecticut's highest court based its decision on the failure of Skakel's attorney to seek out an additional alibi witness.

Skakel's lawyers have argued their client did not commit the crime and was unfairly tried.

Moxley's mother said Monday she was disappointed with the Supreme Court's decision. Dorthy Moxley, 86, who now lives in New Jersey, said she has no doubt that Skakel killed her daughter and she wants to see him back in prison, but will support whatever decision Connecticut prosecutors make about whether to retry him.

"The state of Connecticut had a very, very, very good case, and we absolutely know who killed Martha," she said. "If Michael Skakel came from a poor family, this would have been over. But because he comes from a family of means they've stretched this out all these years."

Skakel is the nephew of Robert F. Kennedy's widow, Ethel Kennedy.

Skakel's appellate lawyer, Roman Martinez, said he hoped Connecticut prosecutors would decide against retrying Skakel.

"Over the past 10 years, two Connecticut courts - including the Connecticut Supreme Court - have painstakingly reviewed every detail of Michael Skakel's case," Martinez said. "Both reached the same conclusion: Michael's conviction violated the U.S. Constitution."

Skakel's case has spent nearly two decades winding its way through the court system after he was charged in 2000 with Moxley's killing. After a jury convicted Skakel, he argued that his lead trial lawyer did an inadequate job representing him, including by failing to contact an additional witness who could confirm his alibi for the time of the killing.

Skakel says he was watching an episode of the "Monty Python" television show at his cousin's house at the time Moxley was killed. Moxley was beaten with a golf club that belonged to Skakel's mother.

Skakel served more than 11 years in prison before being freed on $1.2 million bail in 2013 when a judge overturned his conviction, citing errors by his lead trial lawyer Michael Sherman, who has defended his work.

Connecticut's Supreme Court reinstated Skakel's conviction in December 2016, ruling 4-3 that Skakel was adequately represented. But that decision didn't last.

The Connecticut Supreme Court justice who wrote the majority opinion, Peter Zarella, retired immediately after the decision was announced, and Skakel asked that the decision be reconsidered. A new justice, Gregory D'Auria, sided with the three justices who had previously dissented and in May reversed the court's original decision. It is that ruling that the Supreme Court left in place, turning away the case without comment, its usual practice when it declines to hear a case.