MURRYSVILLE — 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 told a Pittsburgh newspaper: “I don’t know of those phone calls.”