get a frigging lawyer, nobody have time to wipe your shxxt

My suggestion is:  

If you can get the compensation from gas company for rental loss then give his deposit back.

If gas company refuse to give you compensation (because of 9/11 gas shutoff), then don't give his deposit back.

Don't play detective yourself, link his deposit to gas company rent loss compensation.  That way you are not the bad guy. 

You really could have skipped over the first half of your story.