A still image from video footage courtesy WPXI-TV shows stabbing suspect Alex Hribal dressed in a hospital gown after his arraignment with Sheriff's deputies in Export, Pennsylvania April 9, 2014. Hribal, 16, was charged as an adult with multiple counts of attempted homicide and assault in the stabbing rampage that left 22 people wounded at his high school, the Franklin Regional High School in Murrysville, Pennsylvania on Wednesday, a police official said.Photo/Agencies]

MURRYSVILLE - A 16-year-old student wielding two knives went on a stabbing rampage in the hallways of a Pittsburgh-area high school on Wednesday, wounding 22 people before he was tackled by an assistant principal, officials said.

The attacker moved furtively through Franklin Regional High School halls, stabbing his victims in the torso and slashing their arms and faces, students and officials said. Some of the injured taken to nearby hospitals were in critical condition, doctors said.

Alex Hribal, a 16-year-old sophomore, was taken into custody, said Captain Rob Liermann of the Murrysville Police Department.

Charged as an adult, Hribal faces four counts of attempted homicide and 21 counts of aggravated assault, Liermann said, and was ordered to face a preliminary hearing in seven to 10 days.

Students described a scene of panic, with the school hastily evacuated after a fire alarm was pulled.

"He did it so stealthily that at first no one knew what was happening," said freshman Josh Frank. "We heard a girl scream bloody murder. Then two seniors were running down the hall and we followed them out of the school."

The attacker, described by a classmate as a quiet person who kept to himself, started his rampage at around 7:13 a.m. EDT (1113 GMT), walking along the hallways to several classrooms at the school in Murrysville, 20 miles (32 km) east of Pittsburgh, officials said.

Assistant Principal Sam King tackled the boy, who was armed with two straight knives about 8 to 10 inches (20 to 25 cm) long, and an armed security officer handcuffed him with help from King, said Murrysville Police Chief Thomas Seefeld.

People wait outside Franklin Regional High School in Murrysville, Pennsylvania, April 9, 2014. [Photo/Agencies]