Get a lawyer, and take the lawyer with you to the interview.
"Get a lawyer, and take the lawyer with you to the interview."
I second what Keith said, to the letter. And don't get any old atty either, call around and get one familiar with this sort of stuff. At least get a real criminal defense attorney. Maybe you'll waste some money, but I would not undergo any interview with any LEO without an attorney, guilty, innocent, whatever. Provide the atty with whatever they gave you, even if it is just a business card. Oh yeah, and make sure these people really ARE FBI agents.
I find it hard to think this has anything to do with DU. You didn't threaten John Kerry's life, did you? If not I'd think you were OK.