CNN
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When a 19-year-old gunman opened fire at a St. Louis school Monday, killing two and injuring several others, he was armed with a long gun and nearly a dozen high-capacity magazines – enough ammunition for a “much worse” situation, police said.

Authorities credited locked doors and a quick police response – including by off-duty officers – for preventing more killings at Central Visual and Performing Arts High School.

“This could have been much worse,” police Commissioner Michael Sack said. “The individual had almost a dozen 30-round … high-capacity magazines on him. That’s a whole lot of victims there.”

But the tragedy is still devastating for the victims’ families and the entire community, he said.

Student Alexandria Bell, 15, and teacher Jean Kuczka, 61, were killed in the shooting.

Alexandria was looking forward to her Sweet 16, her father told CNN affiliate KSDK. Kuczka was looking forward to retiring in a few years, her daughter told CNN.

The gunman died at a hospital after a gun battle with officers, Sack said. He was identified as Orlando Harris, who graduated from the school last year.

Across the country, at least 67 shootings have taken place on school grounds so far this year.

As the shooting unfolded in St. Louis, a Michigan prosecutor who just heard the guilty plea of a teen who killed four students last fall said she was no longer shocked to hear of another school shooting. “The fact that there is another school shooting does not surprise me – which is horrific,” Oakland County Prosecutor Karen McDonald said.

“We need to keep the public and inform the public … on how we can prevent gun violence. It is preventable, and we should never ever allow that to be something we just should have to live with.”

Alexandria had an outgoing personality, loved to dance and was a member of her high school’s junior varsity dance team, her father Andre Bell told KSDK.

Her friend Dejah Robinson said the two were planning to celebrate Halloween together this weekend. “She was always funny and always kept the smile on her face and kept everybody laughing,” Robinson said, fighting back tears.

Kuczka, a health and physical education teacher, was looking forward to retiring in the next few years, her daughter Abigail Kuczka told CNN.

“Jean was passionate for making a difference and enjoyed spending time with her family,” Abigail Kuczka said in a statement.

Alexis Allen-Brown was among the alumni who fondly remembered Jean Kuczka’s impact on her students. “She was kindhearted. She was sweet. She always made you laugh even when you wasn’t trying to laugh,” Allen-Brown said.

“She made you feel real, inside the class and out. She made you feel human. And she was just so sweet.”

In her biography on the school’s website, Kuczka said she had been at Central VPA High School since 2008. “I believe that every child is a unique human being and deserves a chance to learn,” she wrote.

Seven other teens were injured, some with gunshot or graze wounds. One had a fractured ankle. They were all in stable conditions, the police commissioner said.

It’s unclear how the gunman gained access to the school. Authorities have said the doors were locked.

The police commissioner declined to detail how the shooter got in. “I don’t want to make this easy for anybody else,” Sack said.

The gunman didn’t conceal his weapon when entering the school, Sack said.

“When he entered, it was out … there was no mystery about what was going to happen,” the commissioner said. “He had it out and entered in an aggressive, violent manner.”

Adrianne Bolden, a freshman at the school, told KSDK that students thought it was a drill until they heard the sirens and saw their teachers were scared.

“The teacher, she crawled over and she was asking for help to move the lockers to the door so they can’t get in,” Bolden said. “And we started hearing glass breaking from the outside and gunshots outside the door.”

Adrianne told KSDK that the class stayed put until students saw their assistant principal come up to one of the classroom’s locked windows. “We opened it, the teacher said to come on, and we all had to jump out the window,” Bolden recalled.

Math teacher David Williams told CNN everyone went into “drill mode,” turning off lights, locking doors and huddling in corners so they couldn’t be seen.

He said he heard someone trying to open the door and a man yell, “You are all going to f**king die.”

A short time later, a bullet came through one of the windows in his classroom, Williams said.

Williams’ classroom is on the third floor, where Sack said police engaged the shooter.

Eventually, an officer said she was outside, and the class ran out through nearby emergency doors.

Security personnel were at the school when the gunman arrived, St. Louis Public Schools Communications Director George Sells said.

“We had the seven personnel working in the building who did a wonderful job getting the alarm sounded quickly,” Sells said.

Sack said he did not know if the security guards at the school had guns.

“Not all of the public safety security officers are armed,” the police commissioner said.

He did say the school doors being locked likely delayed the gunman.

“The school was closed and the doors were locked,” Sack told CNN affiliate KMOV. “The security staff did an outstanding job identifying the suspect’s efforts to enter, and immediately notified other staff and ensured that we were contacted.”

After widespread controversy over the delayed response in confronting school shooters in Uvalde, Texas, and Parkland, Florida, Sack said responding officers in St. Louis wasted no time rushing into the school and stopping the gunman.

“There was no sidewalk conference. There was no discussion,” Sack said. “There was no, ‘Hey, where are you going to?’ They just went right in.”

A call about an active shooter at the high school came in around 9:11 a.m., according to a timeline provided by the commissioner.

Police arrived on scene and made entry four minutes later, at 9:15 a.m.

Officers found the gunman and began “engaging him in a gunfight” at 9:23 a.m. Two minutes later, officers reported the suspect was down.

Asked about the eight minutes between officers’ arrival and making contact with the gunman, Sack said “eight minutes isn’t very long,” and that officers had to maneuver through a big school with few entrances and crowds of students and staff who were evacuating.

Police found the suspect “not just by hearing the gunfire, but by talking to kids and teachers as they’re leaving,” Sack said.

As phone calls came in from people hiding in different locations, officers fanned out and searched for students and staff to escort them out of the building.

Officers who were at a church down the street for a fellow officer’s funeral also responded to the shooting, the commissioner said.

A SWAT team that was together for a training exercise was also able to quickly load up and get to the school to perform a secondary sweep of the building, Sack said.

Some officers were “off duty; some were in T-shirts, but they had their (ballistic) vests on,” the commissioner said. “They did an outstanding job.”

Correction: An earlier version of this story gave the wrong age for 15-year-old Alexandria Bell, who was killed in the shooting.