Pittsburgh stabbing incident caused 20 students to get injured after one of their classmates at Franklin Regional High School brought a knife and attacked others.

According to the Star Tribune, the alleged 16-year-old suspect was flailing away with two knives and with a “blank expression” on his face stabbed and slashed 19 students a security guard in the crowded halls of the suburban Pittsburgh high-school Wednesday before an assistant principal tackled him.

The Star Tribune reports that at least five students were critically wounded, including a boy who was on a ventilator after a knife pierced his liver. The attacked only missed his heart and aorta by only millimeters, doctors said.

The incident, which came after decades of U.S. schools focusing their security measures to respond to mass shooting threat or scenarios and not stabbings, has caused a screaming stampede at the high-school. The attacked left blood on the floor and walls, and brought teachers rushing to help the victims.

The alleged suspect’s name is still being withheld and the motive for the attack under investigation. The teenager was taken into custody and treated for a minor hand wound. Late in the afternoon, he was brought into court in shackles and a hospital gown to face charges, Star Tribune reports.

The bloody incident occurred in the morning just minutes before the start of classes at the 1,200-student Franklin Regional High School, an upper-middle-class area 15 miles east of Pittsburgh.

The incident was over in about five minutes, which the boy ran wildly down about 200 feet of hallway, slashing other students with knives about 8 to 10 inches long, police said.

“It was really fast. It felt like he hit me with a wet rag because he I felt the blood splash on my face. It spurted up on my forehead,” Nate Moore said, a 15-year-old student who witnessed the event.

Moore said that he was the alleged suspect tackle and stab a freshman. He attempted to break it up when the boy got up and slashed his face, requiring 11 stitches.

Moore added that the boy “had the same expression on his face that he has every day, which was the freakiest part.”

“He wasn’t saying anything. He didn’t have any anger on his face. It was just a blank expression.”

Assistant Principal Sam King tackled the boy and disarmed him, and a Murrysville police officer who is regularly assigned to the campus handcuffed him, police said as reported by Star Tribune.