HUNTSVILLE (AP) – Attorneys for an inmate convicted in a prison guard’s death are asking the U.S. Supreme Court to halt his scheduled execution. They want justices to review whether lower courts properly denied a federal civil rights lawsuit that sought additional DNA testing in Robert Pruett’s case and whether a prisoner who claims actual innocence, as Pruett does, can be put to death. The execution is set for Thursday. The 38-year-old Pruett was already serving 99 years for a neighbor’s killing when he was convicted in the 1999 death of corrections officer Daniel Nagle at a prison southeast of San Antonio. Nagle was stabbed repeatedly with a metal rod and an autopsy showed the assault caused a heart attack that killed him. Pruett would be the sixth Texas prisoner executed this year.