But the fact remains that if you take bitcoin which belong to someone else, then you are stealing.
Stealing is when you take someone's coins without their consent. You can't know for sure that they aren't fine with it, so you should try to reach them out. To do this, you address to forums, social media, perhaps even with OP_RETURN messages. If you don't get a response within a normal time span, you can't know their consent. So, taking the coins is as stealing as it isn't.
So let's say you use certain Bitcoin mixer, and you end up with my ''stolen'' coins from that paper wallet, that also makes you a criminal and a thief, right??
Being caught a thief is not relevant to being the thief.