JOPLIN, Mo. (AP) – Assistant Superintendent Steve Doerr happened to be visiting Joplin Memorial Middle School Monday when he witnessed a chilling sight: a student wearing a mask and a trenchcoat, armed with an assault rifle.

The boy pointed the weapon at two students and a teacher, then told Doerr, “Please don’t make me do this.” Doerr responded, “You don’t have to do this, there is another way.”

The 13-year-old seventh grader fired a shot into a ceiling before the weapon jammed, authorities said. The student then left the building, followed by Principal Steve Gilbreth, who called the boy’s location in to the office over a handheld radio.

Police arrested the student, whose name was not released because of his age, as he crouched behind a nearby building. No one was hurt.

School officials said Doerr and Gilbreth helped prevent a potential bloodbath, just weeks after three deadly school shootings in three states.

“I would classify this as a very dangerous situation, a life-threatening situation,” said school superintendent Jim Simpson, who described the exchange between the student and Doerr. “This had all the hallmarks of a school shooting.”

“We were lucky.”

Authorities described the weapon as a Mac-90, a replica of an AK-47 assault rifle, which belonged to his parents.

“We don’t believe he was trying to fire at administrators or students,” said Joplin police officer Curt Farmer.

A note in the student’s backpack indicated he had planted an explosive in the school, which has 750 students, but no bombs were found, police said.

His backpack held military manuals, instructions on assembling an improvised explosive device and detailed drawings of the school.

“This was quite well thought-out,” Farmer said. “He had been planning this for a long time.”

Lt. Geoff Jones said the boy’s motives were unclear. School officials said the student had no major disciplinary problems.

Simpson said police told him the boy had a fascination with the Columbine High School shooting that left 15 people dead near Littleton, Colo., in 1999.

The student was wearing a trench coat – like the student gunmen at Columbine – and had a mask or hood fashioned out of a white T-shirt with two holes cut out for his eyes.

Jones said the boy’s parents kept the weapon in a safe at home.

The parents told police their son apparently knew the combination to the gun safe. Farmer said it is not uncommon for people in the area to own assault weapons.

The shooting happened about 10 minutes before school started.

“A lot of the kids were scared,” said eighth-grader Deron Moore. “After they said on the intercom that there was someone with a gun, I kind of went into shock.”

Joplin, which has about 41,000 residents, is on the Kansas state line about 140 miles south of Kansas City, Mo.

Schools across the country have been on alert since three deadly school shootings in three states in a week.

In Pennsylvania, church bells tolled Monday morning in remembrance of the five young Amish girls killed at their one-room schoolhouse one week earlier.

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