The 19-year-old gunman who killed two people at a St. Louis high school Monday was armed with an AR-15-style rifle and over 600 rounds of ammunition, and left behind a note referencing mass shootings, police said.

St. Louis Police on Tuesday showed an image of the rifle used by Orlando Harris, who died after exchanging fire with authorities.

“He had seven magazines of ammunition on a chest rig that he wore, he also had an additional eight magazines of ammunition in a field bag that he had carried,” St. Louis Police Chief Mike Sack told reporters. “This doesn’t include the number of magazines that he left and dumped on the stairway in the corridors along the way.”

Sack said the shooting could’ve been worse had officers not gotten to the school as quickly as they did.

“This could’ve been a horrific scene,” he said. “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.”

Sack did not clarify how the shooter got access to the weapon but stressed the importance of checking in with individuals who are in distress.

“If you’re aware of an individual who appears to be suffering from some kind of mental illness or distress, and they begin speaking about purchasing firearms or causing harm to others, we encourage you to reach out to somebody and report that so that we can get help to that individual,” he said.

Harris also left a handwritten note in the car he drove to the school, according to police.

Sack read part of the note during the news conference, in which Harris described himself as a loner and made reference to mass shootings.

“So, in reading this, we could see some of what’s going on inside his mind,” said Sack. “He feels isolated, he feels alone, quite possibly angry and resentful of others who have what appeared to him to be healthy relationships and so desired to lash out.”

Harris entered Central Visual Performing Arts High School Monday morning at around 9 a.m. with what police categorized as a long gun at the time.

After a gunfight with authorities minutes later, the gunman was taken into custody and later pronounced dead, a St. Louis police official told reporters.

Jean Kuczka, a 61-year-old health teacher, and Alexzandria Bell, a 15-year-old student, were killed in the shooting, according to officials.

Kuczka was a mother of five, a grandmother of seven and a bike rider who participated in an annual charity event to raise money for juvenile diabetes, which her son has, according to her profile on the high school’s website.

She began working for St. Louis Public Schools in 2002 at the Carr Lane Visual Performing Arts Middle School before she transferred to the high school in 2008 to teach health, personal finance and physical education.

Andre Bell, Alexzandria’s adoptive father who lives in Los Angeles, called losing her “a nightmare,” NBC affiliate KSDK reported.

The 15-year-old sophomore had an outgoing personality and was a member of her high school’s junior varsity dance team, Bell told the news station.

“She was joyful, wonderful and just a great person,” he said to KSDK. “She was the girl I loved to see and loved to hear from. No matter how I felt, I could always talk to her and it was alright. That was my baby.”

A GoFundMe created to help Alexzandria’s family with funeral expenses describes her as “beautiful, talented, and charismatic.”

Sack wasn’t able to provide any update on the multiple other victims injured in the shooting, saying that he’s not aware of any of them being released from the hospital since they were admitted. They were all 15 and 16-year-olds and sustained injuries ranging from gunshot wounds to a fractured ankle and facial abrasions, he said Monday.