CALIFORNIA BRIEFING / SANTA CLARITA

A 15-year-old boy carrying a semiautomatic weapon was arrested on a Metrolink train from the Antelope Valley, authorities said today.

The boy, whose name was not released because he is underage, was toting the assault rifle in his backpack Tuesday and bragging to passengers about the gun, said Sgt. Dean Currie of the Los Angeles County Sheriff’s Department.

A passenger who saw the firearm told the conductor, who called deputies at Metrolink, Currie said. The boy was arrested when the train pulled into the Santa Clarita station at 2:45 p.m., he said. The gun was not loaded and its serial numbers had been scratched off, Currie said.

The boy, who lives in the Antelope Valley, told sheriff’s deputies he was headed to downtown Los Angeles, but he did not say why, Currie said. Investigators did not know why the boy was carrying the gun or where he got it. The boy, who has had run-ins with the law, was booked into Sylmar Juvenile Hall and will soon face illegal weapons possession charges, Currie said.

-- Nathan Olivarez-Giles