CNN
 — 

As a 19-year-old gunman walked through the St. Louis high school’s hallways with an AR-15-style rifle and over 600 rounds of ammunition, frightened students and teachers locked classroom doors and huddled in corners.

Some heard gunshots – and someone trying to open the doors, they recalled.

People jumped from windows.

The attack Monday at Central Visual and Performing Arts High School – at least the 67th shooting on US school grounds this year – would leave two dead: student Alexandria Bell, 15, and teacher Jean Kuczka, 61. Other students would be injured.

And after a gun battle with officers, yet another American school shooter also would be dead – this time a recent graduate identified as Orlando Harris who arrived at the campus with an extensive arsenal and a handwritten note, St. Louis police said.

Like so many stories of carnage at places meant for learning and friendship, the school day had begun just as any other.

But then, the assistant principal’s voice came over the intercom with a signal familiar to children who live with this kind of threat, Alex Macias told CNN affiliate KSDK.

“Miles Davis is in the building.”

It was a signal only heard during active shooter drills.

Soon, Alex and her classmates – in class with her health teacher – heard the gunshots, she said.

The teacher locked the classroom door.

But the gunman managed to “shoot his way in.”

“He did shoot Mrs. Kuczka, and I just closed my eyes,” Alex said. “I didn’t really want to see anything else. But then as I thought he was leaving, I opened my eyes to see him standing there making eye contact with me.

“And then after he made eye contact, he just left.”

Teacher Kristie Faulstich, too, had heard the active shooter alert phrase over the intercom, she recalled.

Within a minute of locking her second-floor classroom door, someone had started “violently jostling the handle, trying to get in,” she said.

After the shooter burst into Kuczka’s room, students started jumping from the windows, Alex recalled.

Among them was 15-year-old Brian Collins, a sophomore who went to the school to study visual arts, his mother VonDina Washington said.

Now, with shots ringing out, Brian escaped onto a ledge.

The school’s Dean of Arts Manfret McGhee ran for his life after a bullet missed him in a hallway, he told KSDK.

He hid in a bathroom, not knowing his own 16-year-old son had been shot.

Soon, he ran to his son’s health class.

“When I first saw him, I saw a massive hole in his pant leg, and all I could think of was, ‘My God, what did he get shot with?’” he said.

McGhee used his belt to stop the bleeding.

After the shooting, FBI investigators found a handwritten note in the car Harris drove to the school.

“I don’t have any friends. I don’t have any family. I’ve never had a girlfriend. I’ve never had a social life. I’ve been an isolated loner my entire life,” the note said, St. Louis police Commissioner Michael Sack said.

“This was the perfect storm for a mass shooter,” he said.

The gunman had his firearm out in the open when he arrived at the school and was wearing a chest rig with seven magazines of ammunition, the commissioner said. He also carried more ammunition in a bag and dumped additional magazines on the stairway and in the corridors along the way.

“It doesn’t take long to burn through a magazine as you’re looking at a long corridor or up or down a stairwell or into a classroom,” Sack said. “This could have been a horrific scene. It was not by the grace of God and that the officers were as close as they were and responded in the manner that they did.”

The police commissioner has credited a quick police response, locked doors and prior training for preventing more deaths.

A call about an active shooter at the high school came in around 9:11 a.m., and officers made entry four minutes later, according to Sack. Some off-duty officers who were nearby attending a funeral for a fellow officer also responded to the scene.

By 9:23 a.m., officers had found the gunman and were “engaging him in a gunfight.”

Two minutes later, officers reported the suspect was down.

Seven security personnel were also at the school when the gunman arrived, but the shooter did not enter through a checkpoint where security guards were stationed, said DeAndre Davis, director of safety and security for St. Louis Public Schools.

The security guards stationed in the district’s schools are not armed, but mobile officers who respond to calls at schools are, Davis said.

The doors were locked, and it remains unclear how the shooter got in, authorities have said.

Sack has declined to provide those details, saying, “I don’t want to make this easy for anybody else.”

When asked if it would have made a difference if the first person to confront the shooter had a gun, Board of Education President Matt Davis said, “The assailant had a high-powered rifle. So much so that he could force himself into a secured building. The building is riddled with bullets.”

“I don’t know how much firepower it would take to stop that person. You saw the police response, it was massive. It was overwhelming,” he added. “… I know what would have been different is if this high-powered rifle was not available to this individual. That would have made the difference.”

Such shootings must not be normalized, Davis said.

“The fact that it takes this level of response to stop a shooting like this because people have access to these weapons of war and can bring them into our schools can never be normal,” Davis said

“This is our worst nightmare. … And it can’t happen again.”

The Saint Louis Public Schools district is planning to add gun safety to its curriculum, Superintendent Dr. Kelvin Adams said.

“Not just reading, writing, and arithmetic, but reading, writing, arithmetic and gun safety. That’s a weird kind of curriculum alignment if you will,” he said.

Helping students understand how dangerous guns are will help protect them in school, in their neighborhoods, “quite frankly, everywhere now,” Adams added.