Updated

A 12-year-old boy charged with bringing guns into a middle school was found out because an assistant principal making rounds heard a cartridge being popped into a rifle inside a bathroom stall, a newspaper reported.

Assistant Principal Jamie Addington (search), who is a hunter, "knew instinctively" that he had heard the sound of a gun being loaded, his wife, Sherry, told The Washington Post.

Sherry Addington said her husband looked under the stall Friday and saw the boy with a loaded .30-06 rifle, another rifle and a shotgun. Shocked, he called police while the school quickly implemented an emergency plan.

With police on their way, Bull Run Middle School (search) Principal William Bixby announced over the school loudspeaker that there was a student with a gun in the school, that a lockdown was being initiated and that students should get under their desks.

No one was hurt and no shots were fired, but the situation had parents and students shaking their heads in disbelief as they returned to the school Saturday to collect items left behind after school officials eventually evacuated the building.

Police charged the boy with possession of a firearm on school property, possession of a firearm by a minor and other charges. He was expected to be arraigned Monday in juvenile court.

Naomi Lewis, 38, a cafeteria worker at Bull Run, was charged with possession of a firearm on school property. Her arraignment also was set for Monday.

Police have refused to say whether Lewis is related to the boy, but news reports have identified her as his mother. Investigators said Lewis saw the guns in her car after she drove with the boy to school, locked them in the vehicle, and told no one.

Police said the boy later used a key to retrieve the weapons without Lewis' knowledge.

Authorities said the boy was spotted with one of the guns and the rest were found later. Prince William County police recovered two rifles and a shotgun.

Friends, neighbors and fellow students described the boy as quiet and polite, but also said he was mercilessly teased about his weight, his glasses and his clothing.

They told the Post he talked at the start of the school year about wanting to take over the school, hold hostages and extort money and a helicopter to fly him out of the country.

"Everybody thought he was joking," said one of the boy's best friends and neighbors, whose mother asked that neither she nor her son be identified.