The defendant at the mass shooting in a Northern California railroad yard that left nine people dead Wednesday -- including the shot -- was caught on camera before that morning leaving work.

The suspected shooter, 57-year-old Samuel Cassidy, could be understood from the surveillance footage wearing safety clothes, a hat, and a mask because he leaves his home about 5:40 a.m.. Then he walks across the vehicle and gets into the driver's seat before driving off.

The footage has been shot by a security camera in the house of his own neigh, Dough Suh, who resides across the road.

Over an hour after, Cassidy went on a shooting rampage in the light railway centre to the Valley Transportation Authority in San Jose where he operates, authorities said.

Santa Clara County Sheriff Laurie Smith stated Cassidy also seemed to have put a timer or slow-burn apparatus to place his house on fire, and police also discovered explosives there. The fire was reported only minutes after the initial 911 calls came from the railroad facility.

No rationale is known for its shooting at this moment.