MURRYSVILLE, PENNSYLVANIA (TIP): A 16-year-old boy with a “blank expression” flailed away with two kitchen knives, stabbing and slashing 21 students and a security guard in the crowded halls of his suburban Pittsburgh high school before an assistant principal tackled him.

At least five students were critically wounded in the attack on Wednesday, including a boy whose liver was pierced by a knife thrust that narrowly missed his heart and aorta, doctors said. Others also suffered deep abdominal puncture wounds. The rampage, which came after decades in which US schools geared much of their emergency planning toward mass shootings, not stabbings, set off a screaming stampede, left blood on the floor and walls, and brought teachers rushing to help the victims. Police shed little light on the motive.

The suspect, Alex Hribal, was taken into custody and treated for a minor hand wound, then was brought into court in shackles and a hospital gown and charged with four counts of attempted homicide and 21 counts of aggravated assault. He was jailed without bail, and authorities said he would be prosecuted as an adult. At the brief hearing, District Attorney John Peck said that after he was seized, Hribal made comments suggesting he wanted to die. Defense attorney Patrick Thomassey described him as a good student who got along with others, and asked for a psychiatric examination.

The attack unfolded in the morning just minutes before the start of classes at 1,200- student Franklin Regional High School, in an upper-middle-class area 15 miles (24 kilometers) east of Pittsburgh. It was over in about five minutes, during which the boy ran wildly down about 200 feet (60 meters) of hallway, slashing away with knives about 10 inches (254 millimeters) long, police said. Nate Moore, 15, said he saw the boy tackle and knife a freshman. He said he was going to try to break it up when the boy got up and slashed Moore’s face, opening a wound that required 11 stitches. “It was really fast. It felt like he hit me with a wet rag because I felt the blood splash on my face. It spurted up on my forehead,” Moore said.

The attacker “had the same expression on his face that he has every day, which was the freakiest part,” he said. “He wasn’t saying anything. He didn’t have any anger on his face. It was just a blank expression.” Assistant Principal Sam King finally tackled the boy and disarmed him, and a police officer who is regularly assigned to the school handcuffed him, police said. King’s son told Associated Press that his father was treated at a hospital, though authorities said he was not knifed.

“He says he’s OK. He’s a tough cookie and sometimes hides things, but I believe he’s OK,” Zack King said. He added: “I’m proud of him.” In addition to the 22 stabbed or slashed, two people suffered other injuries, authorities said. The security guard, who was wounded after intervening early in the melee, was not seriouisly hurt. “There are a number of heroes in this day. Many of them are students,” Gov. Tom Corbett said during a visit to the stricken town.

“Students who stayed with their friends and didn’t leave their friends.” As for what set off the attack, Murrysville Police Chief Thomas Seefeld said investigators were looking into reports of a threatening phone call between the suspect and another student the night before. Seefeld didn’t specify whether the suspect received or made the call. The FBI joined the investigation and went to the boy’s house, where authorities said they planned to confiscate and search his computer. “They are a very, very nice family. A great family. We never saw anything out of the ordinary,” said John Kukalis, a next-door neighbor for about 13 years. While several bloody stabbing rampages at schools in China have made headlines in the past few years, schools in the US have concentrated their emergency preparations on shooting rampages.