We've all read stories about unbalanced people coming to work, or their former work place, and doing very violent things. Sometimes weeks or months after being fired.

It seems to me that this situation is potentially far too dangerous to just hope it'll wear off. Especially if he's made threats in the past.

Does he have any guns, or easy access to them? Even if not, that's little comfort because they're not that difficult to get.

It seems to me that your company has to get someone who's expert (at least as expert as someone can be in predicting future behavior) in this stuff involved quickly. Someone needs to have him evaluated by an expert and see whether he's really just joking around. (Though anyone who could joke about such a subject these days, on multiple occasions, at work, with potential victims at hand, seems to me to well worth keeping a very close eye on.)

Get some help somehow. This is serious. Maybe even for himself and the rest of his family as well. Don't put it off.

I'm no expert, but I've been around violent people. You need to get help.

Cheers,
Scott.