Presumably they could ask the car thief where the records came from if they caught him, but it seems likely that the police found the car but have no idea who stole it. In which case, the records are just random objects with no identifiable owner.
(author) They actually arrested the record-dealer out of the car, so they do know who was selling them. Still possible that the seller got them from a middleman or a chain of middlemen though.
Have you considered posting on Craigslist (or Facebook or similar) to see if anyone in the area just had a bunch of records stolen -- and could name some of the ones not obviously pictured in your blog post?
Sure, they might objectively be junk, but they also might be somebody's junk, and returning it to them may make them very happy.
