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Police have identified the gunman in the attack at a private Christian school in Madison, Wisconsin, on Monday as a 15-year-old student, as they investigate the latest school shooting that devastated an American community and claimed the lives of a staff member and another student demanded.

Natalie Rupnow — who was known as “Samantha,” said Madison Police Chief Shon Barnes — was found dead when officers responded to Abundant Life Christian School. There is evidence that the shooter died of a self-inflicted gunshot wound, Barnes said at a news conference late Monday.

Police said six other people were injured in the shooting, including two students who were hospitalized in critical condition.

As the victims recover, authorities are investigating Rupnow’s background, examining writings allegedly linked to her and tracing the history of the weapon she used.

We know that.

Investigators’ “top priority” is to determine the shooter’s motive, Barnes said at a press conference Tuesday afternoon.

“But at this point it appears that the motive was a combination of factors,” he said, declining to provide further details.

Authorities were aware of a “document” that was “widely shared on social media,” the chief said.

“At this point we cannot verify its authenticity,” the chief said. “Today we have detectives working to find out where this document came from and who actually shared it online.”

Police are also investigating the shooter’s activities online, Barnes told reporters. Officials are not releasing “details of these social media accounts,” but he encouraged anyone who knew the shooter or had insight into her feelings before the shooting to contact investigators.

Police said the gunman used a handgun in the attack – a weapon whose history is now being traced by the Bureau of Alcohol, Tobacco, Firearms and Explosives, Barnes said.

“We have asked our partners at the ATF to expedite what we call an ATF traceability form to determine the origin of this weapon, who purchased it and how it got from a manufacturer to the hands of a 15-year-old girl.” , Barnes told CNN’s News Central on Tuesday. “These are questions that will take some time to answer.”

Rupnow’s family is cooperating with police, Barnes said Monday, acknowledging that a heavy police presence at a north Madison home was linked to the shooting.

It’s unclear whether the shooter’s parents owned or owned the gun used in the shooting, Barnes told CNN. The police, together with the public prosecutor’s office, “will want to examine whether the parents may have acted negligently,” he said.

“But at this point that doesn’t appear to be the case.”

Both federal and Wisconsin law generally prohibit possession of a firearm by anyone under 18 years of age. State law also prohibits anyone from intentionally selling, renting or giving away a dangerous weapon to a person under 18 years of age. However, there are exceptions that allow minors to possess a firearm for target practice under adult supervision and for use in the armed forces or for hunting.

Wisconsin also has a child firearm access law that makes it illegal to recklessly keep a loaded firearm within reach or easy access of a child under 14 years of age.

Prosecutors have taken steps in recent years to hold accountable parents who provided their children with the guns they later used in school shootings, testing the limits of accountability.

Two such cases followed school shootings at a high school in Oxford, Michigan, in 2021 and at a high school in Winder, Georgia, in September.

CNN’s Michelle Watson, Eric Levenson and Holly Yan contributed to this report.