[samstave]

Question:

Assume the year is 1790.

DannyBee and PG are having a conversation in a sewer beneath Boston. DannyBee tells PG that he is going to rob the town bank and set it afire.

This was a verbal communication between the two.

There was a USG agent around the corner in another tunnel. He heard an echo of the two talking. This is the only evidence of the two communicating about the matter.

How is this prosecuted?

(please forgive the weak analogy - and improve if you can... but please tell me the 1790 equiv argument for what we are dealing with where the snooping is either protected or denied)