Keith Srakocic, Associated Press
Alex Hribal, the suspect in the stabbings at the Franklin Regional High School near Pittsburgh, is taken from a district magistrate after he was arraigned on charges in the attack on Wednesday, April 9, 2014 in Export, Pa.

GREENSBURG, Pa. — A 17-year-old boy charged in a stabbing rampage at his high school is responding well to mental health treatment and remains hopeful his criminal charges will be moved to juvenile court, his attorney said Friday.

Patrick Thomassey spoke after a brief pretrial conference for Alex Hribal, of Murrysville. He's charged with 21 counts each of attempted homicide and aggravated assault, plus a school weapons violation, for bringing two 8-inch kitchen knives to school and stabbing 20 fellow students and a security guard before classes began April 9 at Franklin Regional High School.

Thomassey acknowledges the boy committed the crimes.

"This is not a whodunit, obviously," he said after Friday's conference. The key question remains where the boy should be tried and how he should be punished or treated as a result, Thomassey said.

A judge gave Thomassey until March 15 to file additional motions, including a request to move the case to juvenile court.

Hribal faces potentially decades in prison if convicted as an adult. But he'd be released no later than 21 if he's convicted in juvenile court. For that to happen, Thomassey would have to convince a Westmoreland County judge that Hribal is more likely to be rehabilitated and be helped by the treatment he'd receive in the juvenile system than in prison.

"Alex is doing much better. These professionals are helping him tremendously," Thomassey said. Hribal is also remorseful, though Thomassey said he still doesn't really know what motivated the boy.

Defense experts who testified at a hearing in September described him as developing schizophrenia and not remorseful.

One of them, psychologist Bruce Chambers, testified that Hribal planned to attack April 20, the 15th anniversary of the Columbine High School shooting massacre in Colorado, but couldn't because school was out that day. Instead, the boy chose April 9, the birthday of Eric Harris, one of two Columbine killers.

Hribal "was planning on this being the end of his life," Chambers testified, "and he was surprised he was still alive after it occurred."

District attorney John Peck said he still believes Hribal should be tried as an adult.

"Based on the facts and circumstances I'm aware of, it should still be a criminal prosecution rather than a juvenile court proceeding," Peck said afterward.

Peck expressed concerns about the court scheduling any hearings on Hribal's juvenile status or other matters on or near the anniversary of the stabbings. Four of the students stabbed were critically injured, though all 21 victims have been released from hospitals.

"This was an extremely traumatic event, and to some extent they're going to relive it on April 9," Peck said.

"Parents have expressed that to me," Peck said, adding he wants to avoid "having to re-victimize these students on or about the anniversary."