The shooter who killed at least two people on Monday at a Christian school in Madison, Wis., was identified as Natalie Rupnow, a 15-year-old student who later died from what appeared to be a self-inflicted gunshot wound, the police said.

The shooter, who went by “Samantha,” opened fire in a study hall classroom with students from several grades at Abundant Life Christian School, said Shon F. Barnes, the Madison police chief.

Officers arrived after a second-grade student placed a 911 call to report the shooting.

Police in Madison, Wis., are investigating how the 15-year-old school shooter obtained a handgun.

Police Chief Shon Barnes, in an interview Tuesday morning with CNN’s John Berman, said partners at the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are expediting a trace form “to determine the origin of that weapon, who purchased it, and how it got from a manufacturer all the way into the hands of a 15-year-old girl.”

At least two people were killed and six others were injured in a Monday morning shooting at a Christian school in Wisconsin by a teenage girl who opened fire on campus, police said.

Madison Police Chief Shon Barnes said one student and one teacher were shot and killed at Abundant Life Christian School, and also said the gun-wielding teenage student was found dead after she appeared to take her own life.

Chief Barnes identified the shooter Monday evening as 15-year-old Natalie Rupnow, a student at the school who also used the name Samantha/Sam online.