My boss threatened to bring guns to work and shoot everyone.?

My boss has several times threatened to bring guns to work and shoot everyone. He has even gone as far as to describe which guns and what type of ammo he will use. He’s never threatened me personally(to my face) but he has named specific people, and threatened people to their face(they were seasonal immigrant workers from Ukraine so they never really said anything). He has made these threats around numerous employees, and has even been spoken to about it by his superior. The threats have continued since he was talked to, and now he says things like “theres a snitch.” It’s made me extremely uncomfortable to be around, and since I know he’s been spoken to already to no avail, I don’t know what I should do. I feel like it’s illegal to say these sort of things. I'm located in California, in case that makes any difference... thanks