[Jason Abbadon]

Classified, YOU did not fire him- he fired himself.
Look, I have been where you are many times- I really truly think some peole act in a self-destructive way to get fired: flipping off customers, coming in late, etc.
Just present the person with the facts and tell them they screwed up and now it's come to this.
Mention that it's not your call, just your responsibility and that they made it possible for them to still collect unemployment. Push the positive and mention that he was obviously unhappy working there anyway.

Then let it go- a lot of people talk trash when they get fired, but it's usually a defensive thing- a way to cope with the embarassment of it.
If the guy should really come back and make trouble, then he's much more self destructive and unhappy than a free man gets to me without help.

Meanwhile, do some smart things- change all the passwords and combonations on everything and maybe adjust the schedule slightly.
I say this because we have been robbed by former employees that broke in, knowing where everyting of value was and even useing existing door combonations (duh!).

Whatever else, dont feel guilty! This was nothing you could have prevented and you're not responsible for the consequences of his bad actions.