At first, the other students thought a fight had broken out.
The hallway inside the science wing of Franklin Regional Senior High School in Murrysville, Pa., was crowded with students on Wednesday morning, unaware of the chaos that was about to break out.
It was no fistfight. For Mia Meixner, the moment of realization -- and shock -- came when she saw a male freshman, who had fallen from the scuffle, stand up, lift his shirt, and reveal the wounds to his stomach.
"I saw blood gushing everywhere,” said Meixner, 16. “That’s when I knew something was wrong.”
A normal school day then turned horrific, students told the Los Angeles Times in a series of interviews.
Cameron Lazor, 16, said he saw a fellow 16-year-old student -- whom he recognized -- holding what appeared to be two large kitchen knives.
Standing from about five feet away, he watched him struggle with a cluster of boys who were trying to pin him down; he escaped after he wounded one of the boys and began running down the hallway.
“People were in shock," Lazor said. "They thought they were in a fight, and then he started stabbing more people, and everyone started screaming and running. It was frantic, no one knew where to go.”
Students dropped their textbooks and began to run, leaving their tan-colored lockers hanging open. Meixner said the attacker stabbed anyone who was in his way.
He ran into a senior girl in a black jacket who was exiting the cafeteria and stabbed her forearm, Lazor said; the girl stood there in shock for a few seconds before she screamed “Oh my God,” repeatedly, with her arm in front of her face, blood dripping on the floor. Another student ran up to help her as the attack moved away.
Trinity McCool, a sophomore, heard something happening behind her but didn't know what was going on. When she turned around, she saw two boys and a girl on the ground; the girl had a gash in her arm.
Then she saw the attacker. He came toward her -- but then another student, Nate Scimio, got between them and was attacked first instead, McCool said.
After Scimio was gashed, the attacker continued to chase McCool and a friend down the hall for a few seconds before apparently turning away, McCool said. "I later heard screams down the halls, so I assumed he turned around and went the opposite way," McCool said.
At some point a fire alarm was tripped -- some students said by Scimio -- and students began flooding out of the school. Aubrey Livengood, a sophomore, said she was in the library printing a class project with a friend when she saw people running down the hallway, screaming for others to run away.
"Run, run, he has a knife!" an earth science teacher screamed, Livengood told The Times.
After she ran out into the parking lot of the school, Livengood saw victims who appeared to have made it outside the school building, where they awaited help. Outside, students were on the sidewalk bleeding, with school officials and other pupils pressing their wounds with their hands and jackets.
One girl had a "slash from the corner of her cheek to the middle of her cheek,” Livengood said. “There was another student on the grass holding his side where he got stabbed. A teacher was over him applying pressure and screaming for the nurse.”
At some point during the attack -- which left 20 people injured, at least two critically -- a security guard and school employee tackled the 16-year-old boy with the knives, ending the rampage. A school security guard was wounded in the attack.
Parents rushed to the scene as ambulances, police cars and helicopters swarmed to the school. The 16-year-old suspect was taken away in the back of a police car. Shane Molyneaux, a sophomore, told The Times that he knew him.
“He was quiet,” Molyneaux recalled. “He was very smart and had a good future ahead of him. I do not know what his motive would be because he was not bullied.” Lazor said she knew the suspect and described him as shy and anti-social. “He was always standing on the outside,” Lazor said. “But there was never a hint that he was going to snap.”
Meanwhile, hundreds of other students at the school were left to take stock of the attack, which comes after several suicides and car accidents have eaten away at morale. Many took to social media to ask for prayers, to check for medical updates on the victims and to debate what could have possibly motivated a classmate to go on the stabbing rampage.
Livengood was among them. One of her friends had been chased by the attacker, she said; she added that she herself would have been near her locker in the white-and-red-striped hallway where the attack occurred if she hadn’t been printing out her project.
“I think I’m handling this all right, but I’ll be a little on edge for a while,” Livengood said. “But I guess it’s natural to feel a little uneasy after all of this.”
[For the Record 2:22 p.m. PST April 10: An earlier version of this post identified Cameron Lazor as female. Lazor is male.]