Federal prosecutors will typically require an individual to make a “proffer” of any information he or she will provide in exchange for leniency. Any statements made during plea negotiations with the government are generally inadmissible under Federal Rules of Evidence 4101 and Federal Rules of Criminal Procedure 11(f)2.
However, the reality is that any statements offered to the government are usually governed by a proffer agreement and typically are not complete immunity agreements. Most proffer agreements contain language that will allow the government to impeach you with your statement if your subsequent testimony is inconsistent with your proffered statement. Moreover, the government can use the information you gave to conduct further investigations and the information obtained as a result of those investigations may be used against you in other charges.
Therefore, due to the limited protection available, great consideration should be given prior to speaking with prosecutors. It is highly recommended that you consult with a lawyer prior to making any statements to the government.