On Sunday night, Ann Arbor Police shot dead a 40-year-old woman in her home who was reportedly holding a knife. The police were called by the boyfriend of the woman, not yet named, over a domestic dispute, Michigan Live reported."We had an argument. Glass was being broke, so I called the police to escort her out," Victor Stephens said. He expressed disbelief at the officers' use of lethal force. "Why would you kill her? He shot her in the head and in the chest. It was a woman with a knife. It doesn't make any sense."Stevens told Michigan Live that she had a history of mental illness.According to a police report cited by Michigan Live, one officer fired his gun and struck the woman, who was declared dead at the scene. Both the Michigan State Police and the Ann Arbor Police Department have launched an investigation into the shooting, but further details are not currently available. Ann Arbor Police Chief John Seto explained that state police were brought in to investigate as an attempt to provide an "objective, unbiased review of the facts."Stay tuned into the state of policing in America with VICE News' Officer Involved blog.