A 14-year-old boy who admitted that he was planning a Columbine-style attack on a Montgomery County high school was sentenced yesterday to as many as seven years in a juvenile-treatment facility.

Dillon Cossey will remain in the facility until he turns 21, unless the courts decide he has been sufficiently rehabilitated before then, Montgomery County Judge Paul Tressler ruled.

The boy apologized in court for amassing a cache of weapons and plotting the assault on Plymouth Whitemarsh High School. Authorities do not think Cossey was close to pulling it off; he had no ammunition.

"I am very sorry, but I do want to get help," Cossey told the judge. "I also hope that me and my family as a whole can get help."

Dillon had admitted in juvenile court in October that he committed three felonies - criminal solicitation, risking a catastrophe and possession of an instrument of crime.

Dillon, who was arrested in October, felt bullied and tried to recruit another boy for a possible attack at the school, authorities said. He was home-schooled and last attended public school in the seventh grade.

He told a friend that he wanted to pull off an attack similar to the deadly 1999 assault on Columbine High School in Colorado, saying "the world would be better off without bullies," according to prosecutors.

In court, Tressler blamed Michele Cossey for her son's troubles. "You want this kid dependent on you? Go buy a dog, go buy a pet," he told her.

The boy's father, Frank Cossey, said he accepted responsibility as a parent.

"Dillon has a kind heart. He is a good person. He does need help," Cossey testified. "We need help. As parents we made some wrong and bad decisions."

The judge ordered mental evaluations for both parents. Michele Cossey cried as Tressler made clear that reuniting the teen with his parents would depend as much on their efforts to change as it would on the boy's own rehabilitation.

"Your mother loves you, but she's not very good at being a mother," Tressler told the boy.

Authorities said they searched Dillon's home in Plymouth Township and found a 9 mm rifle, about 30 air-powered guns modeled to look like higher-powered weapons, swords, knives, a bomb-making book, violence-filled notebooks and videos of the attack on Columbine.

The Columbine attack, engineered by disgruntled teens Dylan Klebold and Eric Harris, led to the shooting deaths of 12 of their fellow students and a teacher. The pair then killed themselves.

Authorities have accused Michele Cossey of helping Dillon build his weapons stash.

She is awaiting trial on charges of illegally buying him a .22-caliber handgun, a .22-caliber rifle and the 9 mm semiautomatic rifle. *