(Reuters) - The U.S. Supreme Court on Monday rebuffed a bid by prosecutors in Connecticut to reinstate the murder conviction of Kennedy family member Michael Skakel for the 1975 killing of a neighbor in the wealthy New York City suburb of Greenwich.

FILE PHOTO: Michael Skakel reacts to being granted bail during his hearing at Stamford Superior Court, in Stamford, Connecticut November 21, 2013. REUTERS/Bob Luckey/Pool

After the high court’s action, Skakel’s attorney, Roman Martinez, called on prosecutors to drop the case against Skakel, a nephew of Ethel Kennedy, widow of slain former U.S. Senator Robert F. Kennedy.

“The evidence shows that Michael spent 11 years in prison for a crime he did not commit,” Martinez said in an email. “The Supreme Court’s decision rejecting review should end this case once and for all.”

Skakel, 58, was convicted in 2002 of using a golf club to kill his neighbor Martha Moxley in 1975, when both were 15 years old, and served more than half of a 20-year prison term before a judge vacated his sentence.

Prosecutors had petitioned the high court to review last year’s decision from the Connecticut Supreme Court throwing out Skakel’s conviction on the grounds that his trial lawyer made a crucial error.

Their request was backed by 11 states, which argued that the Connecticut court’s ruling, if left intact, would prompt a wave of appeals across the country based on claims of ineffective legal counsel.

State prosecutors must now decide whether to retry Skakel, though any new trial would face the challenge of relying on witnesses whose memories are decades old. In a statement, Connecticut prosecutors said they would withhold comment until the case returns to a Connecticut court at a future date and offered condolences to the Moxley family.

Moxley was found bludgeoned to death by a golf club that was traced to a set owned by Skakel’s mother. The killing went unsolved until former Los Angeles police detective Mark Fuhrman, known for his role in the murder case involving football star O.J. Simpson, implicated Skakel in a 1998 book.

A fresh investigation led to Skakel’s arrest in 2000.

In 2016, the Connecticut Supreme Court reinstated his conviction, only to review its own ruling at Skakel’s request. In the interim, a justice who had voted in favor of upholding the conviction retired and was replaced by another justice who went the other way, flipping the court’s 4-3 decision.

The state Supreme Court found that Skakel’s trial lawyer failed to call a witness who could have testified about a potential alibi.

In their petition to the U.S. Supreme Court, the states said the Connecticut court should have considered the overall performance of Skakel’s defense team, rather than focusing on a single error.