NORRISTOWN, Pa. — A 14-year-old boy admitted Friday that he planned a Columbine-style attack on a suburban Philadelphia high school, which could keep him in juvenile custody for up to 6½ years.

Dillon Cossey's admission came about two weeks after authorities searched his Plymouth Township home and found a 9 mm rifle, about 30 air-powered guns modeled to look like higher-powered weapons, swords, knives, a bomb-making book, explosive devices, videos of the 1999 Columbine attack in Colorado and violence-filled notebooks.

Cossey tried to recruit another boy in the plan, which included chaining shut the doors at Plymouth Whitemarsh High School and backing a car up to the door, Montgomery County District Attorney Bruce L. Castor Jr. said Friday.

Cossey, who was home-schooled, admitted to three felonies — criminal solicitation, risking a catastrophe and possession of an instrument of crime — in Montgomery County Juvenile Court.

The boy will be placed in juvenile custody. The longest he can remain there is until his 21st birthday, although he could be released much sooner.

Dillon Cossey will receive regular evaluations by Judge Paul Tressler.

"I'm going to make it clear to you and your parents, if you get to the point where you're ready to get home, but they're not worthy of having you, I'll send you somewhere else" such as to a relative or foster home, Tressler told Cossey.

Authorities have accused Cossey's mother, Michele, of helping him build his weapons stash. She is charged with illegally buying her son a .22-caliber handgun, a .22-caliber rifle and the 9 mm semiautomatic rifle, which had a laser scope.

Cossey admitted telling a friend that he wanted to pull off an attack similar to the 1999 assault on Columbine High School in Colorado, saying, "the world would be better off without bullies," according to Castor.

Cossey, who last attended public school in the seventh grade, took the stand and answered mostly yes-no questions while glancing occasionally at his parents.

His attorney, J. David Farrell, read from a letter that Cossey wrote earlier this week.

"First off, I would like to apologize for the trouble I caused," the boy wrote. "I realize now that I was not thinking correctly. I want everyone to know that what was in my room does not change what was in my heart."

Castor said Cossey described to police being bullied only a few times, but Farrell believes it was more frequent.

"My investigation has really disclosed that he has been the subject of protracted and profound peer abuse his whole life. It drove him from school," Farrell said.

Authorities do not believe the teen was close to pulling off an attack; he had no ammunition and the boy he approached was the first he had asked for assistance.