 Story highlights The DA says 4 people are in critical condition, including one who was "eviscerated" 
 
 Alex Hribal, 16, faces 4 counts of attempted homicide, 21 counts of aggravated assault 
 
 Teachers use students' hoodies as tourniquets on injured teens, student says 
 
 An assistant principal tackled the accused attacker, authorities say 
 
 A teenage boy wielding two kitchen knives went on a stabbing rampage at his high school in Murrysville, Pennsylvania, early Wednesday, before being tackled by an assistant principal, authorities said. 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. "...We have to make sure that he understands the nature of the charges and what's going on here. "Almost all of them said they didn't see anyone coming at them. Then he saw teachers running into the building and pulling "a couple of more students out," he told CNN. In addition to the 22 who were stabbed or slashed, two people suffered other injuries during the melee, authorities said. "I don't know what I got going down at school here but I need some units here ASAP," one officer can be heard saying. Minutes later in another call, another official, breathlessly, can be heard detailing casualties: "About 14 patients right now." "He had his shirt pulled up and he was screaming, 'Help! On Wednesday, Mia Meixner, 16, said the rampage touched off a "stampede of kids" yelling, "Run! The rampage — which came after decades in which U.S. 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. "He was just kind of looking like he always does, not smiling, not scowling or frowning." "And he had this, like, look on his face that he was just crazy and he was just running around just stabbing whoever was in his way." Meixner and Moore called the attacker a shy boy who largely kept to himself, but they said he was not an outcast and they had no reason to think he might be violent. "He didn't have that many friends that I know of, but I also don't know of him getting bullied that much. Hribal's attorney described him as a "nice young man," who has never been in trouble. The boy had a "blank look," she said. I mean, he's a very young kid and he's never been in trouble so this is all new to him." Hribal's attorney said the family was upset by the allegations. His attorney did not immediately respond to a message for comment. Tackled by an assistant principal 
 
 Assistant Principal Sam King is being credited with bringing to an end the 5-minute rampage that authorities say began about 7:15 a.m. 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. A fire alarm that was pulled during the attack probably helped get more people out of the school during an evacuation order, Seefeld said. Although that created chaos, the police chief said, it emptied out the school more quickly, and "that was a good thing that that was done." JUST WATCHED Students stabbed at Pennsylvania school Replay More Videos ... MUST WATCH Students stabbed at Pennsylvania school 00:47 
 
 Photos: Stabbings at Pennsylvania high school Photos: Stabbings at Pennsylvania high school Stabbings at Pennsylvania high school – Parents and students embrace near Franklin Regional High School, where authorities say at least 20 people were injured in a stabbing spree Wednesday, April 9, in Murrysville, Pennsylvania. Alex Hribal, the suspect in the multiple stabbings at the Franklin Regional High School in Murrysville, Pa., is escorted by police to a district magistrate to be arraigned on Wednesday, April 9, 2014,... (Associated Press) 
 
 Alex Hribal, the suspect in the multiple stabbings at the Franklin Regional High School in Murrysville, Pa., is escorted by police to a district magistrate to be arraigned on Wednesday, April 9, 2014,... (Associated Press) 
 
 Westmoreland County emergency management spokesman Dan Stevens, left, looks on as Franklin Regional School District Superintendent Gennaro Piraino pauses while addressing the media during a news conference... (Associated Press) 
 
 A parent holds hands with a Franklin Regional High School while picking up the student after more than a dozen students were stabbed by a knife wielding suspect at the school on Wednesday, April 9, 2014,... (Associated Press) 
 
 Students walk past a row of buses as they leave the campus of the Franklin Regional School District after more then a dozen students were stabbed by a knife wielding suspect at nearby Franklin Regional... (Associated Press) 
 
 A man and woman walk away from Franklin Regional High School after more then a dozen students were stabbed by a knife wielding suspect at the school on Wednesday, April 9, 2014, in Murrysville, Pa., near... (Associated Press) 
 
 Students and guardians walk to their car from the Franklin Regional Middle School after more then a dozen students were stabbed by a knife wielding suspect at Franklin Regional High School on Wednesday,... (Associated Press) 
 
 Emergency responders gather in the parking lot of the high school on the campus of the Franklin Regional School District where several people were stabbed at Franklin Regional High School on Wednesday,... (Associated Press) 
 
 Students are escorted from the campus of the Franklin Regional School District after more then a dozen students were stabbed by a knife wielding suspect at nearby Franklin Regional High School on Wednesday,... (Associated Press) 
 
 Alex Hribal, the suspect in the multiple stabbings at the Franklin Regional High School in Murrysville, Pa., is escorted by police to a district magistrate to be arraigned on Wednesday, April 9, 2014,... (Associated Press) 
 
 A police officer guards the entrance Heritage Elementary School as students are dismissed after more than a dozen students were stabbed by a knife wielding suspect at nearby Franklin Regional High School... (Associated Press) 
 
 A student and guardian walk to their car from Franklin Regional Middle School after more then a dozen students were stabbed by a knife wielding suspect at nearby Franklin Regional High School on Wednesday,... (Associated Press) 
 
 Mike Kane, a parishioner at the Newlonsburg Presbyterian Church in Murrysville, Pa., works on a sign outside his church that abuts the Franklin Regional School District campus, where more then a dozen... (Associated Press) 
 
 Alex Hribal, the suspect in the multiple stabbings at the Franklin Regional High School in Murrysville, Pa., is escorted by police to a district magistrate to be arraigned on Wednesday, April 9, 2014,... (Associated Press) 
 
 Parents arrive to pick up their children from a nearby middle and elementary school after more then a dozen students were stabbed by a knife wielding suspect at Franklin Regional High School on Wednesday,... (Associated Press) 
 
 At least five students were critically wounded, including a boy whose liver was pierced by a knife thrust that narrowly missed his heart and aorta, doctors said. Hide Caption 12 of 12 
 
 At one point, a female student applied pressure to the wounds of one of the male victims, possibly helping to save his life, said Dr. Mark Rubino, chief medical officer at Forbes Regional Hospital in nearby Monroeville, Pennsylvania, where seven teens were taken for treatment. The injuries were stabbing-related, such as lacerations or punctures, he said.
– A student who was stabbed in the liver remains in critical condition following today's rampage at a high school in suburban Pittsburgh that left 23 others injured and a sophomore in custody. The suspect is 16-year-old Alex Hribal, and he has been charged as an adult with four counts of attempted homicide and 21 counts of aggravated assault. The motive remains unclear, but the AP says police are investigating reports of a threatening phone call between Hribal and another student last night. It wasn't clear which of the two made the call. The accounts of exactly what happened at Franklin Regional High School in Murrysville are still unfolding, but authorities say assistant principal Sam King and a security guard at the school tackled and subdued the attacker in a hallway. Some other details emerging: The attack began in a classroom when Hribal pulled out two 8-inch kitchen knives and began slashing students, reports the Pittsburgh Post-Gazette. He reportedly followed them as they fled into the hallway and stabbed others as he ran. During the assault, the attacker "was very quiet," student Mia Meixner tells CNN. "He just was kind of doing it. And he had this, like, look on his face that he was just crazy and he was just running around just stabbing whoever was in his way." A doctor at a nearby hospital said a female student with "an amazing amount of composure" likely saved the life of one of the more seriously injured male students by applying pressure to his wounds. That appears to be junior Gracie Evans, who recounts to the Pittsburgh newspaper: "My friend was on his stomach, and the other kid who was severely injured was told to sit up. I knew that wasn't right. I said to a few students, we need pressure on this wound, and they gave me some paper towels, and I held pressure on that wound for about 10 minutes." Authorities say 22 people were stabbed or slashed, all but one of them students, and two more students suffered other injuries in the chaos.