A former U.S. solicitor general will help Kennedy cousin Michael Skakel appeal his murder conviction to the U.S. Supreme Court, saying Monday the case will focus on when the charges were filed.

Theodore B. Olson has argued 43 cases before the nation's highest court, including representing George W. Bush in the disputed presidential race of 2000.

Skakel, 45, is serving a sentence of 20 years to life for his 2002 conviction in the 1975 beating death of his Greenwich neighbor, Martha Moxley, when the two were teenagers.

Skakel appealed his conviction to the Connecticut Supreme Court last year, arguing among other issues that the five-year statute of limitations expired when he was charged in 2000. The court unanimously rejected the appeal in January. That decision overturned a 1983 precedent.

The Connecticut General Assembly eliminated the statute of limitations for murder in 1976. The state Supreme Court ruled that because the Moxley murder occurred within a five-year window of that legislation, the change applied to his crime.

Skakel's attorneys argued that the decision violated his due process rights under the U.S. constitution by retroactively applying the law.

"I am confident that our petition will present the United States Supreme Court with compelling reasons to hear Mr. Skakel's case and overturn his conviction," Olson said.

Attorney Hope Seeley, who also represents Skakel, has said the appeal would likely focus on the statute of limitations, evidence not turned over during the trial and the decision to try Skakel in adult court even though he was 15 at the time of the crime.

Prosecutor Jonathan Benedict said he would be surprised if the U.S. Supreme Court agreed to take up the case. The court generally agrees to consider cases that have a wider impact, he said.

"This is a one-of-a-kind case," Benedict said.

The U.S. Supreme Court accepts no more than 5 percent of the cases asking for review, said William Dunlap, a criminal law professor at Quinnipiac University School of Law.

Skakel, a nephew of Ethel Kennedy, also has a petition for a new trial pending in Superior Court in Stamford. That petition is based on a claim by Gitano "Tony" Bryant implicating two of his friends in Moxley's murder. Bryant is a cousin of basketball star Kobe Bryant.