I believe most of the information you have received about contacting an attorney is among your best choices.
Having an employee do these types of things while on company time and company equipment is sometimes a little tricky to prove outright. Have you kept notes on any other behavioral problems with this person ?? If not, I would have him sign papers expressing....under his own power, he resolves you from any responsibility in any of these or any other illegal doings while in your employment.
He could have some recourse.... in that you never told him in writing that these types of things could be done on company time. Although you, I and everyone else knows the rules.... if you haven't properly informed someone of something they can't do... it can be an uphill battle. Hopefully a judge would see through that instantly, but the signed confession, so to speak, would help.
We had an employee whom after quitting... came back in our shop at night [unknowingly to us] about two weeks later.... and took a lot of tools. When we realized the tools were missing we didn't know what had happened. About a month later, he told another employee he had them and would return them, since Kevin found them at his place one day. Later, he then applied for unemployment which we went to court for and everything was found in his favor because he said we fired him wrongfully and I threw my hands up in the air and asked how can this be so ?? While the judicator was telling him what he was going to receive and for how long... I said, if this guy didn't quit..... and I fired his ass, what would make him think he could waltz in our shop and burrow tools without telling me two weeks after all this took place ?? The judge asked him if this was true and he said well, I didn't consider it stealing since I worked there, but the judge asked him what is own your mind that you think you can steal from someone that just fired you ?? So, he didn't fire you ?? Anyway, he was then denied all compensation and was told he was lucky I didn't press charges for what he did, let alone what he said in front of a judge.