Why he did not have a receipt is beyond me.
Not your keys...This is inevitable... https://video.nostr.build/e3ac74d343ada785036fca04baf7923dbec0fb13820e2436761d409a15b31737.mp4
Discussion
Maybe he did? When it is in a bank, legally it isn't your money but theirs
Correct, you are the first creditor to their money.
Either way, he would have a transaction number, date, and amount; making recovery trivial. Not recovering it, when he has proof of the deposit, would be easily actionable to the point that the bank would not consider ignoring it.