Prosecutors in St. Louis County have asked the Missouri Supreme Court to refrain from setting an execution date for Marcellus “Khaliifah” Williams, whose DNA was not a match on the murder weapon. The St. Louis County Prosecuting Attorney’s Office’s conviction and integrity review unit sent a letter last week to the court asking for a delay of six months while the office investigates Williams’ innocence claim. The Jan. 2 letter, publicly disclosed by the St. Louis County Prosecuting Attorney’s Office on Friday, said prosecutors “had concerns about this particular conviction.” The law firm Lathr…