No known target in school stabbings
No evidence has surfaced to show a 16-year-old boy charged over a stabbing rampage at a US high school was targeting any particular student, police said.
The motive for the attack on other students at Franklin Regional High School in Murrysville, near Pittsburgh, remains unknown, Police Chief Thomas Seefeld said.
Reconstructing what happened on Wednesday remains difficult because suspect Alex Hribal is not talking to detectives on the advice of his lawyer, and many victims are still recovering, Mr Seefeld said.
Hribal is accused of stabbing or slashing 21 students and a guard. Eight students remain in hospital with four in critical condition.
A prosecutor earlier said that when Hribal was apprehended, he suggested he wanted to die. The boy said "he wanted someone to kill him", according to Mr Seefeld.
The attacker launched his assaults with a "blank expression", witnesses said, as he lashed out with two kitchen knives before being tackled by an assistant principal.
The rampage in an upper-middle-class area 15 miles east of Pittsburgh came after decades in which US schools have geared much of their emergency planning towards mass shootings.
It set off a screaming stampede, left blood on the floor and walls, and brought teachers rushing to help the victims.
Hribal was taken into custody and treated for a minor hand wound, before being taken to court in shackles and a hospital gown and charged with four counts of attempted murder and 21 counts of aggravated assault.
He was remanded in custody and authorities said he would be prosecuted as an adult.
Defence lawyer Patrick Thomassey, who asked for Hribal to undergo psychiatric tests, described him as a good student who got along with others.