they were not caught because of any ID on the transaction/blockchain.
they instead gave away their ID on an exchange. .. and deposited coins into the exchange. where the exchange connected the two pieces of information. and the exchange reported them for suspicious activity
so yea, if you are converting to fiat. that part is the fatal flaw which can identify you being linked to crypto.
i see, now i know why mostly don't want kyc when it come using exchanges for converting their crypto to fiat because someone can trace them or report them especially if they're very suspicious as well like thus two couple.

well they're very exposed tho if they will gave their ID's so it will be a big lesson for them..