Welcome to FT Padre DeCarter. I'm not sure I understand what exactly has happened or why, but my advice is to quit plotting ways to rip off your "friend" and Delta. If you didn't fly these miles, then that's where your interest in the matter should end. The person into whose account the miles were wrongly deposited has his/her own decisions to make. I'd have to hear a lot more about the specifics of what was mistakenly credited, when the credit(s) first appeared, etc. before I could offer any comments or recommendations. Bottom line though, if that person is intent on keeping the miles, contacting Delta about them is probably the wrong move.