A teenager accused of plotting a school attack will be tried in juvenile court because he has no criminal record and has emotional problems that the system can treat, a prosecutor said in a letter sent Thursday.

Montgomery County District Attorney Bruce L. Castor Jr. sent a letter to a county judge Thursday in which he said he would not seek to try Dillon Cossey, 14, as an adult.

Cossey "suffers from severe emotional and psychiatric disabilities which I believe the juvenile court is in the best position to address," Castor wrote. "I find that he is likely amenable to treatment and supervision by juvenile authorities."

The teen's attorney, J. David Farrell, praised the decision and said Cossey's family was relieved.

"It was a very fair and just decision," Farrell said Thursday.

Cossey, a home-schooled student who was arrested last week, felt bullied and tried to recruit another boy for a possible attack at Plymouth-Whitemarsh High School, authorities said.

He had amassed a stockpile of weapons, including a 9 mm semiautomatic rifle, about 30 air-powered guns modeled to look like higher-powered weapons, swords, knives, a bomb-making book, videos of the 1999 Columbine high school attack in Colorado and violence-filled notebooks, authorities said.

Cossey was charged with solicitation to commit terror and other counts. Castor requested an adjudication hearing — the equivalent of a trial in the juvenile system — for Oct. 26, though Farrell said the date has not been confirmed.

Cossey's mother, Michele Cossey, 46, was arrested last week on charges of illegally buying him three guns. Her preliminary hearing is scheduled for Nov. 1.