Updated

Detectives believe a boy charged with stabbing 21 other students and a security guard at his Pittsburgh-area high school threatened two students by phone before the attack, according to a search warrant. Neither was one of the victims.

The warrant, obtained for the home of Alex Hribal hours after last Wednesday's rampage, said two students received "threatening phone messages and completed calls" from someone believed to be Hribal.

It said the threat of violence contained an expletive.

District Attorney John Peck said the two male students who got the calls were not among those stabbed or slashed in the attack, which occurred minutes before the start of classes at Franklin Regional High School.

Neither Peck nor the warrant say when the calls were made. Murrsyville police Chief Thomas Seefeld previously said investigators were looking into a threatening phone call the night before the assaults.

"The caller is believed to be the actor because of the subsequent conduct of the actor coming to school and attacking numerous individuals," the warrant said.

Seefeld noted Monday that police had not definitively linked the calls to the 16-year-old suspect but were seeking phone records to determine if they came from a phone he could have used.

Defense attorney Patrick Thomassey did not return calls Monday from The Associated Press. But he told the Pittsburgh Post-Gazette, which first reported the contents of the search warrant: "I don't know of those phone calls."

He had previously told the AP that Hribal's parents weren't aware of any threatening calls the night before the attacks.

The warrant indicates detectives seized three video game systems and games, a wooden kitchen knife-holder, some notebook paper believed to contain Hribal's handwriting and two computers.

Four students remained hospitalized Monday, three in critical condition. The fourth was upgraded to fair condition.

The high school's teachers attended a counseling session at a nearby church before returning to the school for the first time Monday, part of a three-day effort by school officials and a hired crisis management team to fully reopen the school for classes Wednesday.

On Tuesday, students and parents will get a chance to see that hallways have been cleaned up and other steps taken to return the school to normal.

Some parents said their children are eager to get back to school.

"That's where he wants to be, to be with his friends," Jeff Mauro said of his son, Jamie, a ninth-grader who witnessed some of the stabbings. "This has been a learning experience that we have to love each other — all of us."

Laura Thompson said her children "seem to think they're going to be fine. But I think it's going to be different when they're back in that environment."

Thomassey has said he plans to waive Hribal's right to a preliminary hearing next week. After that, he said he would ask a judge to move the case to juvenile court, a move prosecutors are expected to contest. Thomassey said that request will be based largely on a mental health evaluation by a doctor he's hired.