Also, from the photo's it is only clear that he has the guys email address, and even if he did have his password I'm not sure what he could do with it without committing a fairly serious offense.
I really have no idea how you would go about contacting this person without putting yourself in a compromised position. I realize that you do not want people to jump to conclusions as to this guys guilt, however, at the very least he would be a leading suspect in the theft of this laptop, and that is not the sort of person I'd meet for a coffee and to talk about him maybe giving back my laptop.
Also, if you emailed the guy and politely asked him to return the laptop how long do you think it would take for him to get rid of it on craigslist or ebay?
Therefore, attempting to get more information on who this person is in order to build evidence that the police might be interested in looking at seems quite reasonable.