No one has definitively stated it was workplace violence that I know of, however they are being careful to keep that scenario in play although there is zero evidence to support it.
The FBI is investigating several possible motives, including workplace violence and terrorism, said David Bowdich, assistant director of the bureau's Los Angeles office, adding that terrorism is "a possibility, but we do not know that yet."
http://www.usatoday.com/story/news/...t-we-know-now-latest-facts-thursday/76712186/
I believe it was an act of pure terrorism. What we don't know are the exact motivations behind it. But regardless, the preparation, the planning , and the execution all point to terrorism.
One of the perps worked for five years for the company that was having the Christmas party. He was at a work related function. He left the work function and came back and shot co-workers.
How do these facts preclude it being a work related shooting?