A 15-year-old boy caught with an assault rifle on a Metrolink train bound for Santa Clarita was arrested Tuesday.
The boy, whose name was withheld because of his age, was being held at the Sylmar Juvenile Hall, said a sheriff's lieutenant at the Santa Clarita Station.
The lieutenant said the boy, who is believed to live in the Antelope Valley, had been in trouble before and was just released from a California Youth Authority facility about a week ago.
A train rider who overheard the boy was bragging about the gun notified the conductor, who called sheriff's deputies. And deputies arrested the boy about 2:45 p.m. Tuesday, sheriff's Sgt. Steve Casaus said.
Casaus said the rifle had been modified to fire in a fully automatic mode, and the serial numbers had been obliterated.
