Sounds like he knew something was wrong, because why did he make the same size withdrawals and gambled it all away in a few weeks? If he is addicted to gambling and has no more control over his finances than it's understandable, otherwise I think it's wrong. If I would ever get a large bank transfer by mistake I would never think about starting to gamble with it heavily. Even if the law wouldn't be clear on that and there could be a chance that I can keep the money. What if the money was send by mistake by some criminals and they find out my name and adress? I am sure they wouldn't be so understanding and accept an apology. And what if the judge orders him to repay all the money, including the one he has lost? It could ruin him financially forever.