Los Angeles (CNN) Passengers on a Greyhound bus were able to overcome and disarm the gunman in a shooting that left one person dead and five injured Monday, authorities said.

Shortly before 1:30 a.m., a man on the bus opened fire while the bus was in the Grapevine, California, area on Interstate 5, CHP spokesman Steve Loftus said.

"Due to some very heroic acts by the passengers, they were able to overcome this subject and disarm him," said CHP Sgt. Brian Pennings. "They were able to escort him off of the bus without further incident."

The passengers also administered first aid to the injured victims, Pennings said.

Authorities say they don't know why the shooter opened fire, but CHP said the incident isn't terror-related. So far, there's no evidence the victims knew the shooter.

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