A 17-year-old Rosemead boy has admitted booby-trapping pens that exploded at two high school campuses and injured three people, telling investigators he did it as revenge for being expelled, a police detective said Thursday.
El Monte police arrested the youth, who attended Rosemead High School, on Wednesday after an anonymous phone tip led them to search his home.
They said they found explosive materials and books he allegedly used to rig ordinary writing pens to detonate when uncapped by unwitting passersby who found them lying on the ground at Rosemead and El Monte high schools.
"He admitted this was stupid," El Monte Police Det. Dennis Miller said. "It's a very serious offense. I wouldn't consider it a prank."
The teen, whose name was not released because he is a minor, was being held at Juvenile Hall on suspicion of using a destructive device and possession of bomb-making components, both felonies. The case will be presented to the district attorney today for possible charges.
The victims suffered minor burns and scratches on their hands and faces.
School officials and police found the randomness and potentially serious physical harm of the acts worrisome.
"It could have turned into something that caused far more injury, and even death, than it did," Miller said.
School officials expressed relief over the arrest. "Obviously we're very happy," said Nick Salerno, an assistant superintendent of the El Monte Union High School District, which includes both campuses. "Honestly, I have no comprehension of why anyone would do anything like that."
Miller said it's not clear why the boy wanted to get revenge for being expelled by harming strangers.
Since his expulsion, the boy has been in an off-campus study program to try to get his diploma, Miller said.
School officials and the detective declined to give other details about the teen, including when and why he was expelled.
When police and the Los Angeles County Sheriff's Department's arson-explosives squad served a search warrant on the boy's home Wednesday, his parents were "very surprised," Miller said. "They didn't know that he'd been doing this. They're nice people and were very cooperative."
The books seized by investigators described explosive-making procedures but did not say how to rig a pen to detonate, Miller said. "Coming up with the idea was his doing," he said.
The incidents started at Rosemead High School on Aug. 24 while students were registering for school. A construction worker on campus picked up a pen near a line of students and it exploded in his hands. In September, another small blast occurred when a female resident of Rosemead picked up a pen just outside the school's fence.
A week ago, a student was injured at El Monte High School when he picked up a felt-tip pen in a restroom.