Livermore High School was locked down for about 30 minutes Friday morning while authorities searched the building for a student suspected of having a gun in his backpack, police said.

A man riding Livermore public transit about 7:10 a.m. called police to report a conversation he overheard between two teenage boys, in which one simulated a gun with his hands and pointed to his backpack saying he had "Brass," Officer Traci Rebiejo said. The man asked the boys what school they attended, and they told him Livermore High.

He watched as they got off the bus and retrieved two bicycles, and then called police as they rode toward the school at 600 Maple St.

Officers responded to Livermore High and found two bicycles matching the description, Rebiejo said. A shelter-in-place was ordered at the school while authorities searched for the boys, who were quickly found in the a classroom.

Police searched the teens' backpacks and found that while neither had a handgun or any other weapon, one did have used rifle and shotgun shells in his bag, Rebiejo said. The teen told police he brought the shells to school to melt down in the metal shop. The lockdown was lifted just before 10 a.m. "We apologize for any anxiety caused by our initial phone call alert," Livermore School District Superintendent Kelly Bowers said in a message to parents, referring to a voice mail mentioning a potential firearm. "However we always err on the side of extreme caution in following our safety protocols and in keeping our community informed."

The boys were reprimanded and released, Rebiejo said. It was not immediately known if either would be suspended.

Contact Erin Ivie at eivie@bayareanewsgroup.com. Follow her at Twitter.com/erin_ivie.