Pennsylvania ? 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 6 1/2 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 guns modeled to look like high-powered weapons, swords, knives, a bomb-making book, 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.