Officials in Madison, Wisconsin are trying to determine why a 15-year-old girl allegedly opened fire at her school, Abundant Life Christian School, on Monday, killing a fellow student and teacher before taking her own life from a self-inflicted gunshot wound.

Police said on Tuesday were interviewing friends and family and examining the online presence of the shooter, identified by police as Natalie Rupnow, to determine what drove her to open fire in a classroom at her private Christian school.

Madison Police Chief Shon Barnes said on Tuesday that investigators are looking into online posts and a possible manifesto that Rupnow, who also went by Samantha, may have left behind: “We have been made aware of a manifesto, if you want to call it that, or some type of letter that’s been posted by someone who alleged to be her friend.”  Barnes said they are also examining Rupnow’s cell phone and computer to see if there were any transmissions between her and someone else, and are looking into how the 15-year-old obtained a gun and whether her parents were negligent.

Barnes told ABC News on Tuesday that The suspect’s parents are cooperating with the investigation: “they were cooperative. Despite this tragedy, they still lost a child. They still lost a member of their family. It is certain that they have probably more questions than anyone because they knew her. They lived with her and so we wanted to get an account from them of what kind of child she was.”

Two students were hospitalized in critical condition with life-threatening injuries, while another three students and a teacher suffered non-life-threatening injuries.

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