A fire that killed five members of a Missouri family was intentionally set by the mother, police said. St. Louis County police announced late Wednesday that a preliminary investigation ruled that the deaths of Bernadine Pruessner, her twin 9-year-old daughters Ivy and Lillie Pruessner, and her children 5-year-old Jackson Spader and 2-year-old Millie Spader was a murder-suicide. Police Sgt. Tracy Panus said in an email that investigators believe that Bernadine Pruessner, 39, set fire to a mattress.