That assumes you're going to just sit there and get caught. Which is certainly what's going to happen if you mouth off instead. Someone who goes out with the intent to commit murder (i.e., malice aforethought or premeditation or whatever language your jurisdiction relies upon) by definition has plenty of planning time to minimize the risk of capture.

I'm not interested in the moral issues. The assumption is that you've been wronged and are angry enough that you've decided to do something about it (the fact that the man in this case supposedly has a mental disability is not relevant). I mentioned numerous other ways of dealing with this kind of problem that do not involve violence; each has its merits. If, however, you've decided that violence is the answer, the way to move forward with that plan is to implement it, not discuss it with others. That should be obvious, and is the point I was making.

There's no excuse for slipshod planning or halfhearted execution. Whether something is morally or ethically right does not alter the basic imperative that it be done well, or not done at all.

I would say that being imprisoned for life is about a million times worse than being fired. Thus unless you can guarantee that your odds of capture are literally a million to one, that's not the way to go. (And judging by recent mass shootings, the chances of escape seem to be pretty near zero.)