A WOMAN has killed her ex-boyfriend after he shot dead her brother and niece during an ambush, according to officials.
The Sian family was walking near Montana’s Glacier National Park on Sunday when Derick Amos Madden, 37, rammed his car into them before he started shooting.
David Siau, 39, and his 18-month daughter, McKenzie, were fatally struck. The baby’s mother Christy Siau, 40, was holding her when she was shot dead and was also wounded.
Madden’s shotgun reportedly ran out of ammunition during his assault on the family, and then attacked his ex-girlfriend Christina Siau, 30, with a knife.
However, Christina, who was critically wounded, fought back and fatally wounded Madden, police say.
David and Christy’s two other small children were present during the attack but escaped injury by running away.
Police said the attack was an “isolated … incident with a clear nexus between the victims and Madden,” who had mental health issues.
Christina and her family are originally from New York but she had been living in East Glacier and her family was visiting her when the assault took place.
She is a physician’s assistant and works at a community hospital serving the Native American community, according to The Daily Beast.
Police have not revealed how exactly Madden was killed, but his sister told the outlet that Christine managed to wrestle the knife away from him and stab him to death.
Glacier County Sheriff’s Office spokesperson Jody Hickey said Madden, originally from Oklahoma, had been working recently in the tourist town of East Glacier.
Madden’s sister Michelle told The Daily Beast that he and Christine had been together on and off for the last 10 years.
He spent some time in the military and was deployed to Afghanistan, according to his sister, who added that his mental health issues stemmed from the experience.
“He had been diagnosed with borderline personality disorder, bipolar disorder, and PTSD,” Michelle told the outlet.
“Combined with him drinking on his meds, he just could not process life.”