MADISON, Wis. — The motive for a shooting that killed a teacher and a student and wounded others at a Wisconsin school appears to be a “combination of factors,” a police chief said Tuesday as he appealed to the public to share what they might know about the 15-year-old girl who attacked a study hall before fatally shooting herself.

Madison police Chief Shon Barnes offered no details about a possible motive, though he said bullying at Abundant Life Christian School would be investigated.

Barnes said police have not confirmed the authenticity of a document that might have been written by Natalie Rupnow and could shed light on her actions.

“Identifying a motive is our top priority, but at this time it appears the motive was a combination of factors,” the chief said.

Barnes gave the number to a tip line for anyone who might have known the shooter and her feelings.

“There are always signs of a school shooting before it occurred. We’re looking into her online activity,” he said.

Besides the deaths, six people were wounded, including two students still in critical condition.

Abundant Life is a nondenominational Christian school — prekindergarten through high school — with approximately 420 students in Madison, the state capital.

Barbara Wiers, the school’s director of elementary and school relations, said when they practice safety routines, leaders always announce that it’s a drill. That didn’t happen Monday, the last week before Christmas break.

“When they heard, ‘lockdown, lockdown,’ they knew it was real,” she said.

Wiers said the school does not have metal detectors but uses cameras and other security measures.

Barnes said police were talking with the shooter’s father and other family members, who were cooperating, and searching the shooter’s home.

“He lost someone as well,” Barnes said of the father. “And so we’re not going to rush the information. We’ll take our time and make sure we do our due diligence.”

The shooter’s parents, who are divorced, jointly shared custody of their child, but the shooter primarily lived with her 42-year-old father, according to court documents.

Barnes said the first 911 call to report an active shooter came in shortly before 11 a.m. from a second grade teacher — not a second grade student as he reported publicly Monday.

First responders training just 3 miles away dashed to the school for an actual emergency, Barnes said. They arrived three minutes after the initial call.

Investigators believe the shooter used a 9 mm pistol, a law enforcement official told The Associated Press.

The official spoke on the condition of anonymity because they were not authorized to discuss the investigation.

Later Monday, children and families were reunited at a health clinic about a mile from the school. Parents pressed children against their chests while others squeezed hands and shoulders as they walked side by side.

Abundant Life asked for prayers in a brief Facebook post. Wiers said they’re still deciding whether they will resume classes this week.

Bethany Highman, the mother of a student, rushed to the school and learned over FaceTime that her daughter was OK.

“As soon as it happened, your world stops for a minute,” Highman said, adding: “You just bolt for the door and try to do everything you can as a parent to be with your kids.”

In a statement, President Joe Biden cited the tragedy in calling on Congress to pass universal background checks, a national red flag law and certain gun limits.

“We can never accept senseless violence that traumatizes children, their families, and tears entire communities apart,” Biden said. He spoke with Wisconsin Gov. Tony Evers and Madison Mayor Satya Rhodes-Conway and offered his support.

Evers said it’s “unthinkable” that a child or teacher would go to school and never return home.

The school shooting was the latest among dozens across the U.S. in recent years, including especially deadly ones in Newtown, Connecticut; Parkland, Florida; and Uvalde, Texas.

The shootings have set off fervent debates about gun control and frayed the nerves of parents whose children are growing up accustomed to doing active shooter drills in their classrooms.

But school shootings have done little to move the needle on national gun laws.

Firearms were the leading cause of death among children in 2020 and 2021, according to KFF, a nonprofit that researches health care issues.

Rhodes-Conway said the country needs to do more to prevent gun violence.

“I hoped that this day would never come to Madison,” she said.

As a makeshift memorial grew on a sidewalk outside the school, families were left wondering how something so terrible could happen at the tight-knit private school that they sought out for its academics and Christian values.

“It becomes a real community, a family in a sense,” said Michael Skalitzky, who has three grandsons enrolled at Abundant Life. “I just could never visualize that happening in that school.”

Abundant Life was founded in 1978 and grew rapidly in recent years, interviews and state records showed, with many families using a state voucher program that covers private school tuition for eligible students.

Plans for a vigil and a prayer service took shape Tuesday.

The New York Times contributed.