Like the title says what are the rules. If I miraculously got a private key to a wallet that had Bitcoin in it but was not mine originally then does that mean I now own the wallet like finders keepers and is there any legality issues with this in the usa,uk,canada,south america. Is this more of a morality should you or should you not.
Good luck finding such thing cause it's hypothetical to happen unless you broke into someone device digitally or physically and get hold of the seeds or privkeys. But if the wallet obtained via later then it's digital crime and you could face severe penalty along with prison time.
There is no point in answering a question that is likely to never happen.