The indictment describes the numerous ways in which the perpetrator managed to obfuscate the insider trading. It didn't stop the USG from finding him and prosecuting him.

No. They got sloppy with at least one big position with suspicious timing. [0]

[0] see infamous tweet about position 24h prior to announcement.

How would one do this?

you're right in that, the illusion of transparency actually gives the sophisticated players cover.

If he used different wallets to buy different coins then the correlation might not have been noticed. Buying coins right before they're listed on Coinbase is still suspicious but it would have been less suspicious at least.

yeah but it was private and presumably a pretty limited number of people knew about it at the time which narrows down the number of potential candidates pretty considerably.

There are so many other ways to do this that are infinitely harder to track. Suppose token X is going to hockey stick. You can short a derivative that shorts X. You can long a derivative that longs X. You can leverage a lending protocol that contains X. Etc.

"Buying X when X will go up" has got the be the most unsophisticated way possible one can leverage insider information. Not to mention a basically guaranteed way to get caught.