PLEASANT HILL -- A group of teens blew up a mailbox with a homemade explosive device Friday night, and officers quickly found the group with another bomb in the parking lot of a high school, police said.

The second device was detonated safely by the Walnut Creek Bomb Squad. No one was injured.

Residents in the area of Christine Court reported hearing the first explosion about 9:53 p.m., police said. A witness said a red Chevrolet S10 Blazer left the area shortly after the explosion.

An officer responding to the area spotted the car about 20 minutes later in the parking lot of College Park High School, a few blocks away. He found the second explosive device and detained five juveniles.

Two of the juveniles were arrested on suspicion of explosives possession. A third was arrested on unrelated charges, and two were released into their parents' custody.

Contact Daniel M. Jimenez at djimenez@bayareanewsgroup.com. Follow him at Twitter.com/DMJreports.