JOLIET, Ill.—A judge on Monday delayed for three months a hearing on former suburban Chicago police officer Drew Peterson’s request to toss out his murder conviction in the killing of his third wife after his attorney said he needed more time. Will County Judge Edward Burmila set the next hearing date for May 18. During a brief hearing, Assistant Public Defender Jason Strzelcki told the judge he needed time to interview witnesses, several of whom live outside Illinois. He also said he planned to amend the petition that Peterson filed himself last year. “We will be adding several claims,” said Strzelcki, who did not detail what those might be. The judge’s decision keeps alive Peterson’s legal effort to vacate his 2012 conviction of first-degree murder in the 2004 slaying of Kathleen Savio. He was sentenced to 38 years in prison. Savio’s body was found in a dry bathtub in her …