Your bank files a SAR. An LEA is interested. They come and pick up the supporting documentation and get very interested, interested enough to prosecute.
If the system is working properly, they issue a subpoena or summons for the documentation they already obtained from you and anything else they can think of. Your customer is notified of the demand and has a chance to fight it. (He will lose.) Thus, when the documents provided in response to legal compulsion are introduced into evidence in the prosecution it is very clear how the LEA came into their possession.
If documentation is entered into evidence, but the record shows no paper trail for how the LEA obtained it, then it should be very, very obvious to the customer's attorney that 1) your bank filed a SAR and 2) gave the supporting documentation to the LEA. Your bank has been outed.
Say "Thank you" to any offer of a subpoena or summons for supporting documentation. The LEA is covering your assets, not theirs. They already had the evidence they need and they obtained it legally.
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.