Seems like a weird decision for a hacker to buy ETH with his stolen funds. I mean i would probably buy stablecoins with it in this turbulent market. Also i don't think it is a very good move to buy Ethereum as a hacker because ETH can be pretty easily traced by the authorities, the policy and everyone else. So if he ever wants to cash those ETH out he will probably get caught i think. Maybe he just bought that ETH now to leave them untouched or to stake them for a few years and then in the futures when no one really thinks about that hack anymore he will start to move those funds again. I am sure though that a lot of people will continue to monitor this hacker even in a few years.