The investigation into a shooting at Abundant Life Christian School in Madison, Wisconsin, on Monday that left three dead, including the suspect, continued Tuesday.

Madison Police Chief Shon Barnes said Tuesday the shooting was reported to 911 by a second grade teacher. Previously, he had said a second grade student called 911.

Officers, including some who were doing active-shooter training nearby, responded within minutes.

Natalie Rupnow, a 15-year-old student at the school, was identified as the suspect late Monday. Barnes said she died on the way to the hospital from what appeared to be a self-inflicted gunshot wound.

Another student and a teacher were also killed. Two students remained in critical condition Tuesday while three other students and a teacher suffered non-life-threatening injuries. The victims have not been identified.

Barnes said they believed Rupnow had been at school earlier in the day and there was no indication a breach had occurred. The shooting occurred in a study hall, not a classroom or hallway.

It remains unclear what grade Rupnow — who also went by “Samantha” — was in, Barnes said. The chief has also dismissed rumors the shooter was transgender.

“I don’t think that whatever happened today has anything to do with how she or he or they may have wanted to identify,” he said.

Rupnow had no prior criminal history, Barnes said. A motive for the shooting and how she obtained the handgun used in the shooting were still under investigation.

A “combination of factors” motivated the shooting, Barnes said Tuesday without getting into specifics. He added that investigators have asked students if bullying was an issue at the school.

A handgun was discovered at the scene. Federal investigators are assisting in tracing the weapon’s origin. Parents of suspected school shooters have faced criminal charges in multiple instances in recent years. Barnes said several times Monday and Tuesday that the suspect’s family was cooperating with investigators.

“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 told CNN on Tuesday. “We haven’t been able to locate that person yet, but that’s something we’re going to work on today. We’ll also be looking through her effects, if she had a computer or cellphone, to see if there are any transmissions between her and someone else.”

However, later on Tuesday, Barnes said nothing had been confirmed.

“Again, we are working to authenticate the document that you see online that some are referring to as a manifesto.”

Madison Mayor Satya Rhodes-Conway similarly urged patience.

“There is so much that we do not know and we have to allow law enforcement the time and space for a careful and methodical examination,” she said. “We don’t know nearly enough yet.”

According to reform advocacy group Everytown for Gun Safety, fewer than 5% of school shooters are female.

The school was scheduled to begin holiday break next week and it’s unknown when classes will resume.

Abundant Life Christian School is non-denominational and has about 420 students in grades K-12.

The shooting occurred less than two weeks after a man with a history of mental health issues opened fire on playing children at the Feather River School of Seventh-Day Adventists in Oroville, California. Two boys were seriously wounded before the shooter turned the gun on himself.

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