I can't provide any tx proof, but I've been seeing on Twitter that the hacker allegedly fucked up and made an extremely rookie mistake by sending a certain amount of the stolen funds on a centralized wallet. Hence apparently why this hacker has suddenly had a change of heart and is now trying to be a white hat lol.
The person who was able to get access on that much amount of money should be at least smart enough to not make such a mistake (send funds on a centralized wallet). He isn't white hat too, as NeuroticFish mentioned, he could just ask for the reward in exchange of telling the bug or he could just gain access on it to prove himself that he is "strong" and then just ignore the thing. I think, he understood that it's not the early years of crypto, when it was very hard or impossible to track the transactions (realized it later) and prefer to not spend the whole life in jail + make some self-promotions by this act (media writes about him).