PHILADELPHIA (AP) — A home-schooled teenager who felt bullied amassed a cache of guns, knives and explosive devices and tried to recruit another boy for a possible school attack, authorities said Thursday.

The 14-year-old was taken into custody after police searched his bedroom in a Philadelphia suburb Wednesday evening. He had talked about mounting a Columbine-type attack at Plymouth Whitemarsh High School, authorities said.

The weapons included a 9 mm assault rifle that the teenager's mother had recently bought for him, Montgomery County District Attorney Bruce L. Castor Jr. said. Prosecutors are reviewing her actions.

Police also found about 30 air-powered guns, swords, knives, a bomb-making book, videos of the 1999 Columbine attack in Colorado and violence-filled notebooks, Castor said. The weapons were plainly visible in the boy's bedroom, Castor said.

Also discovered were seven explosive devices Castor described as homemade grenades.