Two people were killed and seven others injured after a former student opened fire Monday in a St. Louis high school before he was fatally shot by police, officials said.

The gunman, identified as 19-year-old Orlando Harris, fatally shot a 61-year-old woman and 16-year-old girl at Central Visual and Performing Arts High School, St. Louis Police Department Commissioner Mike Sack said in a news briefing.

The gunman graduated from the school last year and has no prior criminal history, Sack said. He had almost a dozen 30-round, high-capacity magazines on him, Sack said.

“This is a heartbreaking day for all of us,” Sack said. “It’s gonna be tough. While on paper we may have nine victims… we have hundreds of others. Everyone who survived is going to take home trauma.”

Eight people, including the gunman, were taken to the hospital, Sack said. The woman died at the hospital, and the girl died at the school. The suspect also died at the hospital, he added.

Officers were still in the process of notifying victims’ families Monday evening, said Sack, who declined to identify the victims.

Mass killings database:Revealing trends, details and anguish of every US event since 2006

The seven injured were stable and included male and female students ages 15 and 16, Sack said. Injuries ranged from a broken ankle to shrapnel and gunshot wounds, he said. One student was shot in the leg, one in the arm, and one had a gunshot wound to both hands and his jaw.

Officers were trying to determine a motive, Sack said. “There is some suspicion that there may be some mental illness that he was experiencing,” Sack said.

Sack described a rapid law enforcement response to the incident early Monday. Officers received a call for an active shooter at 9:11 a.m. local time, he said. Officers arrived four minutes later and “immediately” entered the school, where students informed the officers there was a shooter “armed with a long gun,” Sack said.