Police have identified and charged a 16-year-old boy accused of stabbing and slashing 21 fellow students and a security guard at a Pennsylvania high school on Wednesday.
Alex Hribal was charged as an adult following the early-morning attack in Murrysville, 15 miles east of Pittsburgh.
He appeared before Magisterial District Judge Charles Conway and was charged with four counts of attempted homicide and 21 counts of aggravated assault. He was shackled by his hands and feet, and dressed in a hospital gown.
At least eight students wounded in the attack remain in critical condition in nearby Forbes Regional Hospital, according to hospital spokesman Jesse Miller. All the patients there were male.
Three of the students were still in the operating room as of 11 a.m. EDT Wednesday, said Forbes' chief medical officer, Mark Rubino, in a news conference televised on Al Jazeera. Two of them were stabbed in the lower abdomen, Rubino said. Hospital officials later said the third student had a knife wound to the chest that missed the heart and aorta by millimeters.
The University of Pittsburgh Medical Center (UPMC) system treated 11 patients at four different hospitals, UPMC spokeswoman Wendy Zellner said. One 17-year-old at UPMC East had sustained facial wounds.
Most of the victims had been released to their parents by 12:30 p.m. EDT.
Zak Amsler, a 17-year-old junior at the school, said the attack occurred just before his first class was scheduled to begin.
"I saw a girl with blood running out of her sleeve," Amsler said as he waited to pick up his younger sister, a student at the nearby middle school. "It was pretty mind-blowing."
Dan Stevens, the county deputy of emergency management, said later in the morning that the scene had been contained. "The students that are here are safe," he told reporters.
Police Chief Thomas Seefeld said a student or staff member at the school pulled the fire alarm when the attack began.
"The fire alarm being pulled probably assisted with evacuating the school," he said.
School officials and Murrysville police didn't immediately return calls seeking further details, but the school issued a bulletin on its website saying: "A critical incident has occurred at the high school. All elementary schools are canceled, the middle school and high school students are secure."
The district serves about 3,600 local students. The elementary and middle schools are part of the same campus.
The high school was initially placed on lockdown and students were kept there as a precaution as school and law enforcement officials checked the premises.
District Attorney John Peck said he was monitoring the situation, and detectives from his office were also investigating.
Pennsylvania Gov. Tom Corbett pledged his "full support" to law enforcement in a statement on his website.
"As a parent and grandparent, I can think of nothing more distressing than senseless violence against children," he said.
Al Jazeera and wire services