If a person has already been granted use immunity does that mean they are already a government witness or is it a bargaining tool?

When a prospective witness informs the Government he (or she) will refuse to answer questions because the answers might be incriminating, the prosecutor can apply to the Court for an order of use immunity to compel the witness' testimony. Once granted, the witness will have to answer the questions, and the Government will not be allowed to prosecute them for any crimes based on evidence directly or indirectly derived from their testimony. This preserves their constitutional right against self-incrimination. If the witness continues to refuse to answer questions, the prosecutor can move to have them held in contempt and sent to jail until either they decide to answer the questions -- or until the Court determines that no amount of jail time will change their mind. The length of time the witness can be jailed is the amount of time left in the term of the grand jury that is investigating the case. Federal grand juries sit for 18 months. If the case is transferred to a new grand jury, the person could remain jailed while the new grand jury is in session. A witness with use immunity may still be prosecuted, but only based on evidence the Government establishes is not gathered from the protected testimony, but was obtained from legitimate sources independent of his or her testimony. Often, the Government will offer use immunity as a bargaining tool to obtain the witness' testimony and cooperation voluntarily. However, it also may request immunity to force a witness to testify when he or she does not want to cooperate. Either way, if a person has been granted use immunity, the Government is clearly intending to make him a witness, and unless he is willing to serve a jail sentence for refusing to comply with the immunity order, he will have no choice but to be a witness.