US investigators would actually have to get on the foreign exchanges to do an investigation.
Somewhat related, I downloaded the decentralized exchange, bisq.
It's pretty interesting in that you can see the amount of trades daily. US dollar trades are around 15 per day.
I went ahead and set up a sell order in baht for my gf to test it out in Thailand. Set it at 10% though so no bites.
It's not that great but at least a start.