Murrysville, Pennsylvania (CNN) -- Four of the 20 students wounded in a knife attack at a Murrysville, Pennsylvania, high school remained in critical condition Friday, area hospitals said.
The four boys -- ages 15, 17, and two 16-year-olds -- were in intensive care, with the possibility of additional surgeries to try to save their lives.
Only the first hints of a motive have begun to emerge about why 16-year-old Alex Hribal allegedly went on a rampage at his school, swinging two kitchen knives.
In addition to the 20 students who were injured, one adult suffered injuries.
Besides the four patients in critical condition, four others remained hospitalized in fair condition, medical officials said.
Hribal's attorney suggested 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.