Ask Martha Stewart what happens when you co-operate with investigators. If this does not make the hair on the back of your head stand up nothing will!!!
It is crucial to note that affirmatively declining to discuss the investigation in the absence of counsel is not the same thing as remaining completely silent. If you are not in custody, your total silence, especially in the face of an accusation, can very possibly be used against you as an adoptive admission under the Federal Rules of Evidence.
Your invocation of counsel, however, cannot be used against you at trial. United States v. McDonald, 620 F.2d 559, 561-64 (5th Cir. 1980). Your refusal to talk substance in the absence of counsel will force the prosecutor to decide whether your information is important enough to justify a grand jury subpoena for your testimony.