The police and prosecutor take that a person is in possession of the goods stolen in a burglary as evidence of that person's participation in that burglary. One in possession would then be (very likely) charged with burglary and possession of stolen goods. Then it would be up to a court trial to determine whether or not the individual caught with the goods had committed the burglary, had legitimately acquired them, or was trading in stolen goods. This is where the defense arguments - such as, I found that laptop computer on the sidewalk, and took it with me - would become important.
Only in your imagination has the conviction occurred, since such defenses as having found the stolen objects or even that one that you are scorning, that there was a pawn shop receipt verifying a purchase with legitimate intent, must be considered at trial. I am sure that finding a (stolen) laptop or a diamond ring on the sidewalk - and not it turning in to authorities - would be a great defense in some jurisdictions. You tell me where, though.