The religion of peace may have struck California. The story seems suspicious... making it seem work related. But California is a practical gun-free zone. No way he got that hardware in California, or in short time. Some long-term planning had to be involved.
I'm thinking maybe it was both? The hardware used suggests he and his wife were part of a terrorist cell. But maybe something at work triggered a case of Sudden Jihad Syndrome™. Perhaps he was terribly triggered by the yearly Christmas party.
Wouldn't that be some black comedy plot... some drunk coworker set them off and prevented a larger terrorist attack.
It's sounding like that's exactly what happened. There are indications this guy was working with ISIS: http://www.npr.org/sections/thetwo-way/2015/12/04/458464907/alleged-san-bernardino-attacker-pledged-allegiance-to-isis