(ST. LOUIS) -- A 19-year-old former student was armed with an AR-15-style rifle and more than 600 rounds of ammunition when he opened fire at a St. Louis, Missouri, high school on Monday morning, killing two and injuring several others, according to authorities.
The suspect, who also died during an exchange of gunfire at Central Visual and Performing Arts High School, was identified by police as Orlando Harris, who graduated from the high school last year.
Harris, who had no criminal history, left a handwritten document in his car speaking about his desire to "conduct this school shooting," St. Louis Police Commissioner Michael Sack said at a news conference Tuesday.
Sack said Harris wrote: "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." Sack said Harris called himself an "isolated loner," which was a "perfect storm for a mass shooter."
Authorities said Monday there are "suspicions that there may be some mental illness that he was experiencing."
The two slain victims have been identified by the school district as 15-year-old student Alexzandria Bell and 61-year-old physical education teacher Jean Kuczka.
Seven other victims, all 15 or 16 years old, were injured and hospitalized. All were listed in stable condition, according to St. Louis police.
Sack said Harris had seven magazines of ammunition on a chest rig and had eight magazines of ammunition in a bag.
"This doesn't include the number of magazines that he left dumped on the stairway in the corridors along the way," he added.
The shooting was reported at about 9:10 a.m. local time, police said.
Authorities did not say how the gunman entered the building but police stressed that the school's doors were locked. On Tuesday, an official said he did not enter the school through a checkpoint.
Seven security guards were in the school, according to St. Louis Schools Superintendent Kelvin Adams. Officials said security staff identified the suspect’s efforts to enter the school and immediately notified other staff.
"This could've been a horrific scene -- it was not, by the grace of God," Sack said Tuesday.
"It's very easy to get guns," Sack said at a news conference Monday. "I've said it before -- the gun laws in Missouri [are] very broad ... they can carry them openly down any street, and there's really nothing we can do."
St. Louis Mayor Tishaura Jones said she had visited students when the school year started.
"They were bright eyed, bushy-tailed. We laughed, we sang, we danced. And now to be here for such a devastating and traumatic situation breaks my heart," she said. "I'm heartbroken for these families who send their children to our schools hoping that they will be safe. Our children shouldn't have to experience this."
White House press secretary Karine Jean-Pierre addressed the shooting at Monday's press briefing, saying, "We need additional action to stop the scourge of gun violence."
"Every day that the Senate fails to send assault weapons ban to the president's desk, or waits to take ... other commonsense actions, is a day too late for our families and communities impacted by gun violence," she told reporters.
At Tuesday's news conference Sack encouraged anyone to notify police if they are "aware of an individual who appears to be suffering from some kind of mental illness or distress," and is talking about buying guns or causing harm.