Teen girl's motive unclear in Wisconsin Christian school shooting

Police in Wisconsin on Tuesday were interviewing friends and family and examining the online presence of a 15-year-old girl to determine what drove her to open fire in a classroom at her private Christian school, killing a fellow student and a teacher before taking her own life.

The shooter, identified by police as Natalie Rupnow, who also went by Samantha, was a student at the Abundant Life Christian School in Madison, Wisconsin, the state capital.

Women and girls are far less likely to perpetrate both school shootings and mass shootings than male attackers.

Among the 2,610 incidents since 1966 tracked by the K-12 School Shooting Database in which the gender of the shooter is known, female suspects were responsible for only 107. Only about 3 per cent of all US mass shootings are perpetrated by females, studies show.

The motive for the attack remains unclear. Madison Police Chief Shon Barnes told CNN on Tuesday that investigators are looking into online posts and a possible manifesto that the shooter 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.

Barnes said police are also examining her cell phone and computer to see if there were any transmissions between her and someone else. Other questions investigators are trying to answer are how the 15-year-old obtained a gun and whether her parents were negligent.

"That's a question that we'll have to answer with our district attorney's office," Barnes said. "But at this time, that does not appear to be the case."

Police have confirmed the street of the shooter's home in Madison. Online records show someone named Jeffrey Rupnow lives on the same street, and a Facebook profile belonging to a Jeff Rupnow in Madison shows photos of a newborn daughter named Natalie Lynn from 2009, 15 years ago.

Rupnow's cover photo, posted in August, shows what appears to be a teenaged girl trap shooting with a shotgun at a local club. In a comment on the site, Jeff Rupnow says he and his child joined the club in the spring and "have been loving all every second of it."

Rupnow could not be reached for comment.

In the photo, the girl is wearing a T-shirt of the German band KMFDM. The teenaged shooters in the 1999 Columbine school massacre in Colorado were known to be avid fans of the band, and one of the killers posted the band's lyrics on his website.

At the time, KMFDM issued a statement condemning the attack, expressing sympathy for the victims and affirming its music was intended to stand against violence.

Two students were in critical condition with life-threatening wounds, while several other victims suffered less serious injuries.

School shootings have become a near-daily occurrence in the United States, with 322 of them this year, according to the K-12 School Shooting Database. That is the second highest total of any year since 1966 - topped only by last year's total of 349.

Polling shows American voters favor stronger background checks on gun buyers, temporary limits on people in crisis and more safety requirements for gun storage at homes with children. Yet political leaders have largely declined to act, citing the US constitutional protection for gun owners.