Authorities are investigating a domestic murder-suicide in Dallas. Police said 35-year-old Brad Armstrong shot and killed his 22-year-old ex-girlfriend Heather McCarthy Thursday afternoon after the couple had broken up. Then Armstrong fatally shot himself. Police spokesman Sgt. Bill Gorman said the couple had been together for about a year until McCarthy ended the relationship two weeks ago. Gorman said relatives told police that Armstrong was physically abusive and had attacked McCarthy days before the breakup. Gorman said police had no reports of domestic violence between the couple.