(CNN) -- A teenager tackled by a vice principal refused to drop the knives he'd used to stab 21 at his Pittsburgh-area high school, yelling, "My work is not done, I have more people to kill," according to a criminal complaint released Friday.
While several were hospitalized and some underwent surgery, none of the 20 fellow students and one adult stabbed died because of their injuries.
Their alleged attacker -- 16-year-old Alex Hribal -- was eventually disarmed, handcuffed and taken into custody.
On Friday, Westmoreland County District Attorney John Peck told CNN that Hribal is charged with 21 counts of attempted homicide, in addition to other charges like having a weapon on school property.
This reflects a change from the four attempted homicide and 21 aggravated assaults counts he had previously faced. In all cases, he is being charged as an adult.
Hribal stands accused of rampaging through the halls of Franklin Regional Senior High School early on the morning of April 9, using a pair of 8-inch kitchen knives to slash those in his path.
His parents and classmates insisted afterward that they didn't see the horror coming, with lawyer Patrick Thomassey describing him as a well-liked and "typical young kid" who had "never been been in trouble."
Who is Alex Hribal?
Authorities looking through his locker said they found "a document" signaling his intentions to kill, according to the criminal complaint.
One part of it read: "I can't wait to see the priceless and helpless looks on the faces of the students of one of the 'best schools in Pennsylvania' realize their previous lives are going to be taken by the only one among them that isn't a plebeian."
Franklin Regional Senior High indeed has a strong academic reputation. According to the Pennsylvania Department of Education, its students' average SAT scores for 2013 was 1603.
The school is located in the middle-class enclave of Murrysville, a community of about 20,000 people located roughly 20 miles east of Pittsburgh.
In less than five minutes, the scene at the school transformed from a regular morning to sheer terror, as students bled, screamed and -- in a few notable cases -- rallied to help one another.
The rampage ended when Assistant Principal Sam King spotted the suspect holding the knives as well as as a security guard, Sgt. John Resetar, bleeding nearby.
Assistant principal who tackled suspect hailed as 'great man'
According to the criminal complaint citing the school administrator, Hribal was "facing Resetar (when King) grabbed the accused from behind and took him to the floor."