That's not necessarily true, Jumbo. The witness's statement is basically "It wasn't me, I had nothing to do with it." I can see a reason why an attorney would want to get this in for the truth of the matter - i.e. that the witness indeed had nothing to do with the crime. The inference would then be that, if the witness had nothing to do with it, perhaps the D also had nothing to do with it. Thus, it would be hearsay, although the practical strength of this inference is a bit silly. So, because it could be hearsay in that instance, we need to find an exception. The one that immediately came to mind was coconspirator hearsay, assuming there is a conspiracy charge in there. But I don't think that would work because, in this posture, it would be self-serving to the D, the one seeking to introduce the statement.
That's just a long way of saying that Jacy et al. are right - have fun with impeachment, cuz that's all you got.