This is attorney protected information. We've been having discussion with a legal person about being interviewed by law enforcement officials and/or signing a statement. These comments are offered by permission (and might be coupled with DCF's advice of saying only "I Want a Lawyer"): [Begin comments]
What do you mean, that they would use the information to "impeach" a possible witness? Do you mean that he would not be called to testify against a defendant?
Sorry to be opaque - "impeachment" means, basically, making a witness lose credibility with the jury. The only use I've been able to imagine for wanting a written statement is to make you look bad, in the event that you are called by either side to testify, and end up testifying favorably to the defendant. If you appear to be a "hostile witness", it's even possible that you can be impeached by the attorney/party who asked you to testify. The scenario I see looks something like this - 1. You're called as a defense witness to testify to the effect that you've been on the list for years, messages like the defendants's weren't unique or especially unusual, that you understood them as satire or political commentary and not as actual threats, given the wider context in which they occurred. The general impression conveyed by your testimony is that you're a rational, reasonable, respectable person who the jury can like and trust, that you think the defendant is perhaps weird but basically misunderstood and harmless. 2. The prosecution cross-examines you about your conclusions re the defendant - they're going to ask you how well you really knew/know him, how much you knew about his other behavior (they're likely to try to sneak in information about the defendant's other alleged misbehavior here, if they haven't already), and so forth. To the extent that you say you didn't know him, your direct testimony becomes less and less relevant - and if you start to say that you did know him well, they're likely to produce the document you wrote/signed, and ask you a series of uncomfortable questions about it, designed to create the impression you were lying to the jury earlier during your testimony, e.g., if the statement says "I didn't know that the defendant had done these other creepy things, and they make me question whether or not I know him very well, and I feel differently about his threats now that I know about those creepy things", the prosecutor will make a big production out of pointing out the differences between your testimony at trial and what you wrote during the LEA interrogation. Understandably, you probably wanted to distance yourself from the defendant when the LE agents were in your home, especially after they'd given you a list of creepy things he supposedly did - but they're going to hold you to the same degree of distance from him and his thoughts/actions if you end up testifying at trial. Writing it down and having you sign it serves several purposes - it gives the prosecutor a document s/he can wave around, ask you to read from, and otherwise organize a little production around - it also lets you be impeached with your own words, instead of calling the cops to the stand to dispute your recollection of your conversation, which takes on a "he said/she said" tone, and might make it look like the big mean cops were picking on poor little you. If they can make poor little you eat his own words, they look good, and you look bad. So .. that's what I'm afraid the document is for. I've been trying to think of something else - but especially where the agents asked you to pick out just key bits of your conversation, and assert that they're true, and let the rest of the information be lost to memory and time .. it makes me think the information they selected was important to them. The information they got seems helpful to them only in the context that you end up testifying at trial - I can't think of any other reason it would be useful to them. It sounds like the psychological factors of the questioning were pretty well optimized to make you want (probably partly subconsciously) to distance yourself from the defendant, both to avoid implied guilt by association, and to maintain a common ground of reasonableness with the cops while discussing other things like politics. The current issue of the Utne Reader has a piece by the Unabomber's brother and his wife talking about how the FBI manipulated them into providing evidence against the Unabomber by appearing sympathetic and reasonable, forming a common "us (good people) versus the actions of they crazy guy, who needs us to work together to help him get better" bond which was ultimately used to try to kill the crazy guy, to the horror of the brother/wife. While I do think that they may have pulled a fast one on you, I don't think that reflects badly on you as a person .. it's pretty difficult to tell which cops are actually reasonable people, and which are pretending to be reasonable people in order to further their own agendas. [End comments]