What would you do?

Free legal advice is worth what you pay for it.

Don't entirely agree with Chayro, because truth is an absolute defense to a libel or slander suit, and there are jurisdictional issues - they likely have to sue you in your state and county. It depends on the nature of the "proof" you have, and how you came by it.

Spoken like a true non-lawyer. Truth is a defense you can use after you get sued. The idea is not to get sued in the first place. It's not what you don't know that hurts you - it's what you think you do know. Be careful. It's a dangerous world.

Chayro, I've practiced law for 33 years, so far.

OK, then you know that you don't want to be a defendant in a lawsuit if at all possible. Maybe I'm a bit more risk adverse than you are. Getting sued sucks. They don't teach that in law school.

It is interesting to observe two very different approaches by two lawyers. Not being a lawyer, I can clearly see that both can be combined successfully. You can do things differently depending on the case and the client.
But..I prefer Lloydc's stance overall.