(CBSNEWS) - Witnesses say the attacker did not say anything as he ran through a Pennsylvania high school Wednesday, slashing fellow students with two knives.
The attack at Franklin Regional High School in Murrysville, Pa., left 21 students and a security guard injured. At least three attack victims remain hospitalized.
The school is closed Thursday as officials investigate what motivated the attack.
Shackled and dressed in a hospital gown, Alex Hribal, 16, was charged as an adult Wednesday with four counts of attempted homicide and 21 counts of aggravated assault.
Dan Stevens, deputy emergency management coordinator for Westmoreland County Public Safety, told CBS News' Vinita Nair, "He attacked his classmates; he attacked his friends. We're going to have interview other friends and neighbors and relatives to find out exactly what went on."
Police searched Hribal's home and confiscated a computer, looking for a motive in the vicious attack.
"If my best friend wouldn't have stepped in front of me, I probably would have been injured," student Gracey Evans said. "I probably would have been the one that was stabbed."
Witnesses say the teenage attacker had a knife in each hand and a blank expression as he slashed at anyone in his way. Evans said, "He was just completely silent, said not a word."
Officials say the stabbing could have been much worse if a student hadn't pulled a fire alarm in the midst of the attacker's spree.
Even before emergency crews arrived, students and faculty managed to tackle the suspect.
"We had students helping other students that were laying there bleeding," Stevens said. "We had faculty members attacking the individual, getting him down on the ground. It was a situation where the good overpowered the evil."
The community gathered Wednesday night to pray for the wounded as well as the accused attacker, who classmates are describing as a loner. Student Mia Meixner said, "He just kep to himself and was more quiet. Just didn't really care about what other people did."
Stevens said of Hribal, "They're actually saying he might not even had a cell phone, so there might not be anything that we can find from those type of things. We might not ever know why he did what he did."
Hribal's defense attorney is requesting a psychiatric evaluation, arguing that his client may not even be aware of what he did. The district attorney, on the other hand, is suggesting that Hribal made comments suggesting he wanted to die shortly after he was taken into custody.