Assuming you know something about digital snooping, and he doesn't know anything about privacy, you can figure out a lot about him, possibly even remotely acces

Assuming you know something about digital snooping, and he doesn't know anything about privacy, you can figure out a lot about him, possibly even remotely access your computer and (if it has a webcam) take a picture and report everything to the police. You should talk to the police first (in fact, you should've the moment it was stolen), but explain that you know a lot about computers (most police don't have much in the way of computer security experts on staff, and they wouldn't waste their time on petty theft) and will be trying to find out more about this guy. They'll probably be glad for anything you might find, so long as it's well-documented and provable, and this kind of investigation should be admissible in court. There are reported cases of theft victims snapping pictures of thieves with their webcams and actually getting results. If you feel bad for the guy, and assuming you find him, you can ask the cops to cut him a break if he gives evidence about the thief he bought it from. They will probably offer him this deal too, but since he already reached out to you, he will trust you more when it comes from you.