A day after a Murrysville, Pennsylvania, teen allegedly rampaged through his high school's hallways, stabbing wildly with two kitchen knives, the first hints of a possible motive began to emerge.

The attorney for 16-year-old Alex Hribal raised the specter that his client may have been bullied, telling CNN affiliate WTAE in Pittsburgh on Thursday that it looks like some kind of "bullying event" may have played a role.

"I think a lot of things have happened. I don't want to comment specifically, but I think there are some things that occurred that led to where we are today," Patrick Thomassey said.

But an FBI official, familiar with the investigation, discounted bullying as a motive.

"He was disaffected but not bullied," the official said on condition of anonymity.

Hribal, a sophomore, was charged as an adult and faces four counts of attempted homicide and 21 counts of aggravated assault in connection with Wednesday's attack at Franklin Regional Senior High School that left 20 teens and one adult wounded.

Some classmates at the school describe Hribal as having few friends and being quiet but also as a "really nice kid," a description that contradicts the image of a knife-wielding teen offered by authorities.

Murrysville Police Chief Tom Seefeld said investigators haven't yet made sense of the mass stabbing.

"We believe, through the investigation, that this was random," he told CNN's "New Day." "We don't have anybody that was targeted, as far as we know at this point."

Still, there were more questions than answers about what led the teen to allegedly attack his classmates with two steak knives believed to have been taken from his family's home.

"We're going to try to figure out what happened here. Obviously, there's a problem. You just don't leave and go to school, and do what he did yesterday," Thomassey told CNN earlier in the day.

There is "some deep-rooted problem somewhere that caused him to do this."

One thread that police are looking into is the possibility that there was a phone threat the night before, Seefeld said.

But no immediate evidence has been found to confirm such a call, and Thomassey discounted the allegation.

"He was home all night the night before this occurred, with his parents," he told WTAE. "They did not see him on the phone arguing with anybody."

The FBI has seized electronics belonging to Hribal, including a computer and cell phone, and will analyze them for any clues, the police chief said.

In a telephone call Thursday, President Barack Obama assured Franklin Principal Ron Suvak that the FBI will continue to assist in the investigation, the White House said.

See more on this story at CNN.com.