CENTENNIAL, Colo. - He went to his suburban Denver high school armed with a shotgun and looking for a specific teacher, the local sheriff said.
He wound up shooting two students, one critically, before apparently killing himself.
"The teacher began to understand that he was being looked at and exited the school. One student confronted the armed student and was shot," Arapahoe County Sheriff Grayson Robinson said.
One of the wounded students, a girl, was in serious condition, Robinson said. The other student suffered minor injuries and was expected to be released from the hospital last night, he said.
A suspected Molotov cocktail was also found inside Arapahoe High School, the sheriff said. The bomb squad was investigating the device.
The student with the shotgun wasn't trying to hide it when he entered the school from a student parking area and started asking for the teacher by name, Robinson said.
The teacher then left the school, Robinson said.
"He knew he was the target and he left that school in an effort to try to encourage the shooter to also leave the school," the sheriff said. "That was a very wise tactical decision."
And it all happened a day before the one-year anniversary of the Newtown, Conn., school shooting. Adam Lanza, 20, killed 20 children and six adults at Sandy Hook Elementary School before killing himself.
Deputies and police officers who responded to the school immediately entered to engage the gunman as students were kept locked in their classrooms.
"Within 20 minutes of the time of the report of the shooting, our deputies found the suspect dead inside the school," Robinson said.
Several other school districts in the Denver area went into lockdown as reports of the shooting spread. Police as far away as Fort Collins, about a two-hour drive north, were increasing security at public schools because of the shooting.
At Arapahoe High, students were seen walking toward the school's running track with their hands in the air, and television footage showed students being patted down. Robinson said deputies wanted to make sure there were no other conspirators but now believe the gunman acted alone.
Parents were told to go a church to find their children and stood in long lines. One young girl who was barefoot embraced her parents and the family began to cry. Neighborhoods were jammed with cars as parents sought out their children.
Arapahoe High sits just 8 miles east of Columbine High School, in Littleton, where two teenage shooters killed 12 classmates and a teacher before killing themselves in 1999. The practice of sending law enforcement directly into an active shooting, as was done yesterday, was something that was developed in response to the Columbine shooting.
Tracy Monroe, who had siblings who attended Columbine, was standing outside Arapahoe High yesterday looking at her phone, reading text messages from her 15-year-old daughter inside.
Monroe said she got the first text from her daughter, sophomore Jade Stanton, at 12:41 p.m. The text read, "there's sirens. It's real. I love you."
A few minutes later, Jade texted "shots were fired in our school." Monroe rushed to the school and was relieved when Jade texted that a police officer entered her classroom and she was safe.
Monroe was family friends with a teacher killed in the Columbine shooting, Dave Sanders.
"We didn't think it could happen in Colorado then, either," Monroe said.
Colton Powers, 14, a freshman, said he heard three shots in a classroom. The shots sounded far away, he said.
"We all ran to the corner of the room and turned off the lights and locked the door and just waited, hoped for the best," he said. "A lot of people, I couldn't see, but they were crying.
"I was scared. I didn't know what to do," he said.
His mother, Shelly Powers, said she first got news of the shooting in the middle of a conference call at work.
"I dropped all my devices, got my keys and got in my car. I was crying all the way here," she said.
More than 2,100 students attend Arapahoe High, where nine out of 10 graduates go on to college, according to the Littleton Public Schools website.