Alex Hribal
Alex Hribal has been charged with four counts of attempted homicide and 20 counts of aggravated assaultYouTube

A teenager who allegedly went on a knife rampage at a high school near Pittsburgh, Pennsylvania, has been identified as Alex Hribal.

The suspect, who has been charged with four counts of attempted homicide and 21 of aggravated assault as an adult, is accused of injuring 22 pupils at Franklin Regional Senior High School on Wednesday.

Four pupils were airlifted to hospital in critical condition and the other victims suffered multiple stab and slash wounds, although nobody was killed. The pupils were aged between 14 and 17 and the motive of the attack is not known.

Management at the school posted on its website: "A critical incident has occurred at the high school. All elementary schools are cancelled, the middle school and high school students are secure. Additional information will be released as soon as possible. Please keep our campus clear of traffic."

Who is Alex Hribal?

The suspect is a 16-year-old school pupil at the high school, who has been described by other students as coming from a "good family". Hribal, who lives in Murrysville, was described as a "shy person" who "never seems very upset or anything like that".

Patrick Thomassey, Hribal's attorney, said the suspect's parents were "devastated" when they found out about the incident on the news. He added that there was "no indication there was any reason for this to occur, no sense of trouble about anything".

According to Thomassey, Hribal was a "good student" who "interacted well with other students".

He added: "He's frightened. He's a 16-year-old kid who looks like he's 10."

Does Hribal have a history of violence?

The suspect did not have a history of violence and speaking to the Pittsburgh Post Gazette, one student described Hribal as someone who would "never do anything violent".

Some have reported that Hribal may have been bullied, yet this is disputed among pupils at the school. One student, known as Santino, told the Huffington Post: "One of the kids he stabbed was a good friend of his. He didn't have a lot of friends, but he was not bullied."

Speculations have been made about Hribal's mental health. He was described as having a "blank look" on his face during the attack. Mia Meixner, who witnessed the incident, told CNN: "He was very quiet. He just was kind of doing it. And he had this look on his face that he was crazy and he was just running around stabbing whoever was in his way."

Like others, Meixner said she did not know if Hribal had been bullied: "He kept to himself a lot. He didn't have that many friends that I know of, but I also don't know of him getting bullied that much. I actually never heard of him getting bullied. He was just kind of shy and didn't talk to that many people."

Did Hribal have a history of mental illness?

Authorities have not detailed a possible motive in the attack, but the district attorney said the teenager made "statements" to officials that "he wanted to die". However, Hribal did not have a known history of depression or any other mental illness.

Thomassey said that he would file a motion to juvenile court, as Hribal is currently being charged as an adult.

He said: "I'm not sure he knows what he did, quite frankly. We have to make sure that he understands the nature of the charges and what's going on here. It's important that he be examined by a psychiatrist and determined where he is mentally."