Every so often the defense wants a co-accused to testify because they have something beneficial to say and they have already said it at the Article 32, UCMJ, hearing. As we know, the prosecution almost never willingly immunizes the witness, and judges don't always force the issue. (Odd how that happens to the defense, but never the prosecution.)
Anyway, check out, Federal Evidence Review's, item, Former grand jury testimony of cooperating witness should have been presented to the jury under FRE 804(b)(1); Ninth Circuit adopts broad application of “similar motive” requirement, in United States v. McFall, _ F.3d _ (9th Cir. March 9, 2009) (No. 07-10034).
This is a case where the alleged co-accused's testified to Brady material (my construction of this) at the grand jury hearings in the case. Of course the prosecution objected to having the grand jury testimony of the witnesses played at the accused's trial. The witnesses had invoked their Fifth Amendment privilege at trial. The government wasn't interested in having the witnesses evidence before the jury so they had not called the witnesses themselves, even though the witnesses had agreed to cooperate with the prosecution.
Here, the 9th Circuit adopted a rule that's frequently raised against the defense — the "similar motive" rule.