A killer who was executed in Missouri for the 1987 murder of a 12-year-old girl was also responsible for a long-unsolved triple homicide in Iowa three years earlier, investigators announced Friday. New DNA evidence implicates Andrew W. Six in the 1984 bludgeoning deaths of 20-year-old Justin Hook Jr.; Hook's fiancee, 19-year-old Tina Lade; and Hook's mother, 41-year-old Sara Link, the Iowa Division of Criminal Investigation and Wapello County Sheriff Mark Miller announced. "What we know for sure is that Andy Six is responsible," Miller said at a news conference at his office in Ottumwa, in southeast Iowa.