Odds are they'll get ahold of his computers, phones, correspondence, and financial records to basically figure out where he stuffed the cash by going through the records.

If it is in a bank account abroad, they can seize it with the proper paperwork and court orders. The reach of the US government is considerable, especially when dealing with people are already incarcerated in US prisons. There are some places that don't play ball with the US, but putting money in those places is a considerable risk.

If he tucked it away in a hard drive or some other form of digital storage, they can probably crack that - either the password is something that is similar to his previous passwords and can be figured out with analysis and time, or has he generated a random character password and stored this password somewhere.

I can see guys who steal tens of millions being able to hide some of it, especially if they worked alone -or at least limited their partners- and have a limited digital trail.

SBF stole billions; enough money to make it worth going through every minute of the last decade of his life with a fine-toothed comb, he worked with a ton of other people who have knowledge on his methods (and are young enough to desperately want to avoid spending decades in prison themselves- so they will testify), and he was basically plugged into one device or another at all times.