The decision was another turn in a high-profile case that drew television crews and celebrity crime writers like Dominick Dunne. Judge Thomas A. Bishop set aside the murder conviction of Mr. Skakel, 53, who was sentenced to 20 years to life for killing the neighbor, Martha Moxley, when they were both teenagers in Greenwich.
The 136-page decision amounted to a review of the trial and an attack on the way Michael Sherman, the lawyer who represented Mr. Skakel before he was convicted, had handled his defense.
With a new trial ordered for Michael Skakel, a defense lawyer for the Kennedy cousin serving time in the 1975 slaying of a neighbor said he will seek his release from prison on bond.
Skakel's conviction was set aside Wednesday by a Connecticut judge, Thomas Bishop, who ruled that Skakel's trial attorney failed to adequately represent him when he was found guilty in 2002. Bridgeport State's Attorney John Smriga said prosecutors will appeal the decision.