possible stolen dirt bike?

So heres the deal, i purchased a dirt bike from a kid couple hours away a few months ago. In his craigslist add he stated that it was a 2001 kx100 for $400 and it needed a new top end and parts were in boxes. I figured hey I'm fairly mechanically inclined and it would be a good bike for the girlfriend so i went down to check it out and sure enough, all the parts were in boxes. So i bought it from him for $300 went home and a few months later fixed her all up and realized this is totally not a 2001. So i ran the VIN on a website and it happens to be a 2007 kx 100. I only got a bill of sale with it and his name doesn't exist, I wrote down his cell phone number and tried calling him but it has been disconnected. Anyways, I feel guilty knowing this could have potentially been some kids bike but i really don't want to lose out on all I've put into it. How can i figure out if it truly was stolen without contacting the police?