FINRA, not the FBI, would Blue Sheet the trades. Each clearing firm will submit trade reports to FINRA. That could take all but a few minutes depending on the clearing firms reaction time. When I was doing clearing, I could run a report in seconds on a stock and give it to compliance.
In the report, you run trades, accounts, names, ss/tid numbers, addresses, phone numbers, beneficial owners, trade authority, etc.
So if two guys were washing trades using 10 different firms and multiple shell companies doing so, they can get the information in moments, see the patterns and know exactly who did what.
THAT FAST!!!