DONT ANSWER ANY QUESTIONS WITHOUT A LAWYER!
Best advice I ever had from a lawyer was to shut up and provide just the minimum.
Many years ago I was subpoenaed (sp?) by, of all people, the SEC over some stock I bought and sold from a micro cap. I had called the company a few times to ask about delayed filings and strange stock action, and I think this is what triggered the subpoena.
It seems the company was run by crooks (wish I would have known), and the SEC had probably been tracing phone calls, so they went on a fishing expedition with me to see what they could dig up. The subpoena was extreme legalese, but the bottom line was, send us every record you've ever had for the last five years and we'll decide if there's anything interesting. Phone, bank, email, trades, and so on for myself and my family.
I began filling out an extremely detailed set of questionnaires then stopped and thought, wait a minute, since when does a govt agency have the right to ask a private US citizen, with no connection to a company, for all of this info? So I saw a lawyer, and their advice was to answer their questions but only with the minimum required info -- ie, yes or no. He adviced to not provide any additional info (which I was in the process of providing), not because it was incriminating (since I did nothing wrong), but it would open me up to more questions, more subpoenas, etc.
I followed the lawyer's advice, sent in some yes and no answers, and never heard back from the SEC. The company was shut down a couple of years later and my stock went in the tank, but that was my one and only experience with being on the wrong side of a gummint investigation.