Just a small point but one worth considering I think - the photos causing your suspicions are not on the camera as you say, they are on the card. Card and camera are not inseperable, and many folks have bought cards they believed to be new from t'interwebnet and found photos still on them. This in itself doesn't prove the camera is stolen in my book.
Have you really quizzed the guy you bought it from to see where he got it and why it's so cheap?
I'm sure if you just contacted the police, gave them the serial number, if their checks do not show the camera as stolen, you can relax. If it is stolen, the cops will want you to hand it over, and you should tell them the truth about where you got it - that way the worst that can happen to you is that you will be minus one camera AND $450.