Pull this post and talk to lawyers if you haven't already.

Depending on where you're based you'll have legal obligations that'll define what you should be doing at this point. This may well involve lawyers, your regulators and the police.

Some countries make it a criminal offence if you let a criminal know that you suspect them of money laundering or similar offences (this is known as "tipping off") so you should be very very careful about what you're disclosing both to your users and the general public.