Customer with dda account comes in with large cashiers' check from other local bank. Uses it to purchase several $10,000 (even)cashiers' checks, as well as several lesser cashiers' checks. All cashiers' checks are in the names of the same 4 people as on the original cashiers' checks.

Structuring?

This happened almost two years ago, but the conversion of one of the $10,000 checks to cash and another cashiers' check led me to research the original funding source.

You really don't know at this point. I would monitor checks to see when, where and by whom they are negotiated. I have seen such actions mean nothing (just a way for them to hold money until needed) and I've seen them all cashed the same day; thereby, warranting a SAR for structuring.