A recorded conversation, without a warrant.

[cbg]

Depending on the exact circumstances, it might be that the recording was legally obtained.

 

[quincy]

Definitely any answer to these questions depends on the facts, the most important ones of which are missing here.

If Adam or Barney are charged with a crime, especially if the crime is murder, the best advice is for Adam and/or Barney to hire a good criminal defense attorney. The attorney will ensure that only admissible evidence is used in court.

 

[adjusterjack]

OK, so we're back to: Questions:
1. Ignore it. We now know the identity of Charlie.
2. Is that recording admissible in court?
3. Might Adam be found guilty in Charlie's death?

You are welcome to study a publication called "Can We Tape" which provides the eavesdropping and recording laws of every state.

https://www.rcfp.org/wp-content/uploads/imported/CANWETAPE.pdf

 

[quincy]

Relax, people. . . This IS hypothetical.
... Charlie is the POTUS ...

Now that it's back, the OP needs to tread lightly with his lighthearted, hypothetical situations. "The powers that be" don't take kindly to public threats (even veiled or "hypothetical" ones) made against "Charlie".

Zigner’s post with its warning needs to be emphasized.

Speaking on a public forum, even hypothetically or in jest, about committing crimes against a world leader is not smart. Postings of this type are liable to attract the attention of law enforcement officials.

The attention is drawn to posts not because of super secret surveillance but because some readers may see threats (even when none were intended) and report what is posted to authorities.