The problem is only the prosecutors are usually authorized to grant immunity. Period.
But did these guys know that? Did the folks at State claim they had that authority, or even believe themselves that they did? That's the question. I'd say from what I've read the answer is most likely "yes". And failing to bind the government by that offer would have serious 5th Amendment implications.
thats not true, it is not only prosecutors that can grant immunity, congress grants immunity frequently....the facts of the case are clear, the statements were given under promise of immunity (i believe contractual) because they were forced to give statements to the
government
Under what circumstances does Congress grant immunity, Yurt? And to whom?
While you're figuring that out, go back to first premises. We're talking about a criminal prosecution here. Under the Fifth, nobody can be compelled to testify against himself (or herself). That includes statements under oath in court or statements given to investigators, interrogators or any other government entity eliciting information which could lead to criminal penalties.
The only way testimony can be compelled is under a grant of immunity from prosecution, thereby removing any criminal penalty for the forced testimony. With no possibility of criminal penalty resulting from the testimony, the Fifth is not compromised.
There is no reason to offer, promise or grant immunity other than to compel otherwise self-incriminating testimony - none. With me so far?
Blackwater was employed by the Department of State. No contract to which the State Department is a party, such as the contract between the US Government and Blackwater, can confer immunity for criminal acts. The State Department has no prosecutorial discretion and cannot use contempt powers, only the Department of Justice has that power. Think it through.
Any statement or testimony compelled by a government agent under promise of immunity, even if that agent cannot actually grant the immunity, cannot be used in court as evidence if that person is brought up on criminal charges. Further, no information gained as a result of the tainted statement can be used as evidence. The statement itself is a "poisonous tree", any information gained as a result is its "fruit" and also tainted
From there it gets complicated, but the gist of the ruling here is that the statements were compelled and therefore tainted under the Fifth. The prosecution did not properly insulate the rest of its evidence which resulted in that also being tainted. The judge dismissed the charges without prejudice, meaning if the government can get its act together and try again with clean evidence it is free to do so. I personally hope they can and do.
Sorry about the novel here but if you think about it, it really isn't all that complicated.