NEW HAVEN— Prosecutors want a man convicted of killing a former New Haven alderman and another man in 1990 kept behind bars while they appeal a ruling that his right to a fair trial was violated.Judge Charles Haight Jr. ruled last month that Scott T. Lewis should be released from prison within 60 days unless the state decides to retry him.The defense should have been told that a police lieutenant said the witness who implicated Lewis initially told him he knew nothing about the crime, then later acknowledged the information he gave had been supplied by a detective, Haight said.Prosecutors last week filed a motion seeking a stay of the ruling while they appeal, saying they deserve a chance to appeal the ruling without being forced to retry Lewis simultaneously. Prosecutors contend the defense knew the witness denied knowing about the crime.They also cited an earlier ruling in state court finding that the information provided by the detective to the witness was insignificant.Lewis has been serving a 120-year sentence after he was convicted of the shooting deaths of former Alderman Ricardo Turner and Lamont Fields.He maintains his innocence. Stefon Morant also was convicted in the killings and was sentenced to 70 years in prison.Haight ruled that Lewis’ defense should have been told about the account by former Lt. Michael Sweeney, who said the witness told him that he knew nothing about the murders. Sweeney said a detective joined the interview and began giving the witness facts about the crime and the witness then started changing his statement.Sweeney later confronted the witness, who told him he was not telling the truth and that the detective was the source of his information, according to the ruling.Haight said the fact that the witness told the defense he denied knowing about the crime was not the same as knowing about a claim that a detective coached the witness about the facts of the case.Sweeney said he told a supervisor — but not prosecutors — about his concerns. Haight said he found Sweeney’s account credible and concluded it was central to the credibility of the state’s key witness and that Lewis’ right to a fair trial was violated.If the state decides to retry Lewis and the witness repeats his testimony implicating Lewis in the killings, Sweeney’s account will be available to the defense in challenging the witness’s credibility, Haight said.