The Fifth
Twice recently I've had people - potential witnesses in criminal cases - tell me, "the prosecutor said I couldn't take the Fifth because I'm not testifying to anything incriminating." One of them, an alleged complaining witness, even told me, "the prosecutor said I didn't need a lawyer because he's my lawyer."
Hogwash.
First, the prosecutor isn't the witness's lawyer. He shouldn't be giving legal advice to the witness and he certainly shouldn't be claiming to represent her. The prosecutor represents the government, and if the government's interests clash with the witness's interests, he is going to do what his client, the government, wants him to do. The witness who listens to the government in those circumstances is looking for trouble.
Second, the prosecutor doesn't get to decide whether the answer to a question might be incriminating. Neither does the judge. Nor do the police, the FBI, or the DEA. Only the witness can possibly know what is in her head, and even she isn't competent to know whether what is in her head, if it came out, might incriminate her. For example, if you talk to federal agents, and they decide later that you lied (whether they are correct or not), you can be prosecuted for making a false statement.
If a witness refuses to answer his questions outside court, all the prosecutor can do is subpoena her to court. If she takes the stand and takes the Fifth there and the prosecutor still wants her to answer his questions (at about this time the prosecutor ought to be taking a deep breath and wondering whether he really wants the answers), he must immunize her. That means that he must get a formal order declaring that what she says can't be used against her. If she answers the questions then, fine. If not, he must ask the judge to order her to answer the questions. If she answers the questions then, again, fine. If not, then and only then may she be punished (by being held in contempt) for not answering the government's questions.
Sometimes, maybe, with the advice of a good lawyer who is familiar with all of the facts, it makes sense for a person to give up the protection of the Fifth Amendment and talk to the government. Usually, though, a witness has so little to gain from talking to the government, and the possible legal downside of talking is so great, that the best advice is for the witness to keep her mouth shut at least until not doing so is punishable as contempt.
Who ya gonna believe, me or some guy who's in the business of putting people in prison?