LAFAYETTE - An Acalanes High School freshman was arrested today after he brought a homemade bomb to school and then voluntarily surrendered it to administrators, police said.

"Based on the initial investigation, it appears that there was no intent or plan to commit an act on violence on the school," Police Chief Michael Hubbard said. "We believe -or what we think is - that he forgot it was in his possession and when he made the realization, he turned it in. The problem is that he shouldn't have had it anyway."

The explosive - described as smaller than an apple and similar to a pipe bomb - was safely dismantled by the Walnut Creek Police Bomb Squad off campus. School remained unaffected, with students going about the regular day without knowledge of the incident, Hubbard said.

School administrators sent out a mass e-mail to parents just after noon that said students were notified in a message read during their fourth period class. The letter described the device as a C02 cylinder, which Hubbard could not immediately confirm.

Still unclear this morning is why the boy made the bomb in the first place, and why he brought it to campus, Hubbard said. The boy now is with his parents.

Police will present the case to the District Attorney's Office, which could charge the juvenile with possession of an explosive device on school grounds, a felony.

Hubbard said no one suspected the bomb before the boy gave it to a teacher, who then notified administrators. The school called police at 9:18 a.m. The bomb was capable of injuring people in its immediate vicinity had it gone off. Hubbard said the boy could have harmed or killed himself when he constructed and handled the device.

"Whether or not he meant to construct something that dangerous, the simple fact is that it was a dangerous device," Hubbard said. "It sounds -so far - like it's going to be a kid who made a bad and dangerous mistake."

Malaika Fraley covers crime and public safety. Reach her at 925-945-4782 or at mfraley@bayareanewsgroup.com.