Hmm, based on what you just said, it sounds like he has acquired some information he probably shouldn't have. Being a bit paranoid in this day and age is a good thing IMO. I'd say if it continues for much longer, I'd confront him on it. especially if he slips and says something that no one but you and your attorney should know about. Then again, if he's HR, that's a tough battle. If he was the janitor, it might be a little easier.
Come to think of it, it wouldn't be that difficult to have a friend or something send him an email from an anonymous ***** account advising him of some inappropriate behavior and that he is being monitored. I bet he shuts up real quick.
When I worked at a huge company we used to pull pranks like that with this a-hole in our department (he was ultimately our boss!). We pretended we were women from a dating site. He was in a serious relationship, yet his ego was so huge he'd engage in this dubious online behavior. We never did tell him it was us, and that there were no women checking him out.