The boy was charged on Tuesday in King County Juvenile Court with possessing stolen property, unlawful possession of a firearm and carrying a dangerous weapon to school. He pleaded not guilty.

VIDEO: Todd Beamer Suspect Appears In Court

Gun theft charges have also been filed in Pierce County against two other boys, 15 and 16, accused of helping the boy steal six handguns from a safe in the Puyallup home of a Washington State Patrol trooper. One of the two other boys is the trooper's son.

The 15-year-old was arrested last Thursday after three of the guns were found in his possession at Todd Beamer High School in Federal Way. He told police he planned to sell the guns.

VIDEO: Man Who Stopped School Scare Speaks VIDEO: Extended Interview With Todd Beamer Resource Officer

Investigators found the other three guns in a garbage bin outside the 16-year-old's apartment in Federal Way.

Pierce County prosecutors also expect to file six counts of theft of a firearm and second-degree unlawful possession of a handgun against the 15-year-old, Deputy Prosecutor Fred Wist said.

Previous Stories: April 24, 2007: Officer Who Arrested Student With Weapons Speaks Out April 19, 2007: Police Arrest Student With Guns Stolen From Trooper's Home