Cogdill v. State
In Cogdill v. State, 101 P.3d 632 (Alaska App. 2004) the Court laid out a test for determining whether a defendant is entitled to dismissal of criminal charges when the State fails to offer immunity to a proposed defense witness.
Under Cogdill, the defendant must demonstrate that the trial would be fundamentally unfair without the witness's testimony -- that the proposed witness would provide "crucial, verdict-altering evidence". Id. at 636. If the defendant meets this test, then the trial court must determine whether the State has valid reasons for declining to immunize the witness. Ibid.
The Court noted in Cogdill that the State generally has a valid reason to decline to extend immunity to witnesses who are apparently accomplices in the defendant's criminal acts, and who propose to offer testimony exculpating the defendant -- since granting immunity to such witnesses "would likely engender collusion and witness-tampering." Ibid.