Do they ever use such deals to trick the suspect? I mean, tell the suspect something like, "We feel for you and think you were manipulated, after the fact, and we don't think you were involved in the crime - we you? (suspect lies, says no) and so we'll give you this immunity deal (on, say, possession of the phone) and you give us all you have on PK" and then the suspect, KKL, who thinks she can lie her way out of her culpability, ends up talking too much and implicates herself so immunity withdrawn and she gets charged?