A second-grader called 911 to report the shooting at Abundant Life Christian School in Madison, Wisconsin, on Monday, Dec. 16, Madison Police Chief Shon Barnes said at an evening news conference. The shooter, a teacher and a student are dead. Six others were injured and two remain in critical condition.

“Let that sink in for a minute,” Barnes told reporters. “A second grader called 911 at 10:57 a.m. to report a school shooting.”

Police arrived about four minutes later, Barnes said, explaining that the shooting occurred in a study hall at the K-12 school, according to the Associated Press.

The shooter was identified as 15-year-old Natalie Rupnow, who went by the name Samantha, Barnes said. She was pronounced dead on the way to the hospital. There is evidence that she died from a self-inflicted gunshot wound, Barnes said, according to CNN.

Police will release the victims’ names after all family members have been notified, Barnes added, suggesting the names could be released during the next press conference on Tuesday, Dec. 17, at 1 p.m. CT.

Police responded to an active shooter call at the school shortly before 11 a.m. Monday, Barnes said at an earlier news conference. “No officers fired their weapons,” he said.

The students did “excellent” after realizing it wasn’t a drill, Barbara Wiers, the school’s director of elementary and school relations, said, according to CNN.

“I can’t tell you how well our students did in this process,” Wiers added. “They were visibly scared… When they heard ‘lockdown, lockdown’ and nothing else, they knew it was real, but they did brilliantly.”

The school has 420 students. There are no metal detectors, but Wiers said the school has other security measures in place, including cameras.

The shooter’s family is cooperating with authorities, added Barnes, who said his department is now tasked with determining a possible motive. On Monday evening, Barnes said the shooter’s father spoke to police at one of their facilities. They are not currently considering charges against the parents as they are “fully cooperating,” he said.

“Many of you have asked me why,” Barnes said during the earlier press conference. “Why did this happen? What do we know? What was the motivation? I don’t know it. But I will tell you this: Our detectives are working hard in the investigative process to find out as many answers as possible so that we can continue to prevent things like this from happening not only in this community, but in other communities across our country. “

Two students were in critical condition and had “life-threatening injuries,” Barnes said. Three other students and a teacher suffered non-life-threatening injuries. According to ABC News, two of those four were released from SSM Health St. Mary’s Hospital – Madison on Monday evening.

Want to stay up to date with the latest crime coverage? Sign in PEOPLEis the free true crime newsletter with breaking crime news, ongoing trial coverage and details on intriguing unsolved cases.

After the shooting, schools in Madison were placed on lockdown.

“I think we can all agree that enough is enough,” Barnes said earlier Monday. “We have to do everything we can together to support our students so that press conferences like this don’t happen again and again.”