When I went to the police station to find out if the bike I got was stolen, the first thing they wanted to know was where I got it. I wouldn't tell them. If it was stolen, I wanted it to be returned to it's rightful owner, but that's it. How would you know exactly how the bike got to you? Did the guy who sold it to you steal it? Maybe he bought it from someone else, and only found out it was stolen after he sold it to you. Do you want to get him involved with the police?
Just my opinion.