Santa Clarita Valley Sheriff's Station deputies arrested a juvenile who allegedly boarded a Metrolink train armed with an automatic assault weapon today, a sheriff's official said.

The juvenile, whose name is not being released, boarded the Metrolink train bound for Burbank, without a ticket and allegedy hiding a gun hidden in his backpack, Sgt. Darren Harris said. Another Metrolink rider tipped deputies off about the gun toting teen. Deputies captured the suspect at the Santa Clarita Metrolink station.

"(The suspect) sat right next to me and we started talking," Eric Arismendez said.

Arismendez was visiting his girlfriend in Lancaster for the last time before heading to the United States Marine Corps basic training Jan. 5. He was talking with the suspect about upcoming basic training when the suspect allegedly displayed the gun in the backpack, Arismendez said.

"I asked him how old he was and he said 15," Arismendez said. The suspect's age shocked Arismendez as did another revelation during the train ride.

"He told me he just got out of jail for gun possession," Arismendez said.

The suspect allegedly tried to evade the sheriff's deputies as they canvassed the train for tickets. Arismendez saw his chance to alert the conductor.

"I wrote down (the suspect's) seat number, the car number and what he was wearing," he said. Arismendez handed the information to the conductor who contacted the sheriff's deputies.

Deputies swarmed the Metrolink station at 22122 Soledad Canyon Road at about 2:30 p.m. Tuesday.

Passengers poked their heads out of the stopped trains doors as deputies closed in on the suspect. The baby-faced suspect was arrested, cuffed, frisked and pushed into the back of a deputy car.

The suspect was booked on felony possession of an assault weapon, felony possesion of a machine gun, felony posession of a concealed firearm and felony possession of a firearm with an altered serial number, Harris said. The suspect will be taken to Sylmar Juvenile Detention Center to await a court date, he said.