The first search needn't be illegal. An example: NSA surveillance of a smuggler in Mexico produces the name of Joe Schmoe in El Paso (for concreteness let's sa

The first search needn't be illegal. An example: NSA surveillance of a smuggler in Mexico produces the name of Joe Schmoe in El Paso (for concreteness let's say the intercept is "Joe Schmoe will distribute our cocaine, as always"). The DEA gets tipped, Joe Schmoe's name goes up on a tack board and he's put under surveillance. A case may be built from there using classical police methods.