Based on reports this was not a disgruntled employee incident.
This seems to be a tactical hit where the shooters got away.
That narrows the possible outcomes to militia (motive unsure) or terrorism...or Obama and his gun control agenda gone mad.
Two things have NOT been mentioned, it may have all started because of an offensive video that was put on the Internet, AND, the El Chapo Guzmans men which could be entrenched in San Bernadino some territory battles to score and settle come accounts.