Suspect testimony in the grand jury room

I wanted to add a point of caution about my co-blogger Paul Cassell's view of Officer Wilson's grand jury testimony. I'll assume Paul is right that if the grand jury believed Wilson, then Wilson had a valid self-defense claim. But I'm not sure about an assumption Paul may be making, that a grand jury should take seriously a criminal suspect's exculpatory testimony. Paul writes: "Only if there was good reason to discount [Wilson's] testimony, should the grand jury have returned a true bill."

I'm not so sure. Isn't there always "good reason" to discount a suspect's exculpatory grand jury testimony? A guilty suspect has an obvious incentive to lie. It's particularly easy to lie in a homicide case where the other participant is dead. The grand jury proceeding isn't adversarial, or at least ordinarily is not, so the suspect is not cross examined and the holes in his story will remain unknown. And the fact that Wilson's testimony seems so well-tailored to self-defense law could be seen as highly suspicious, rather than highly exculpatory. Given that, I don't know what grand jurors are supposed to make of a suspect's exculpatory testimony. Maybe they should take it seriously, but maybe they should view it with great skepticism. I'm not sure.

None of this means that the grand jury was wrong if they credited Wilson's testimony. But I don't think it was obviously right for them to do so, either. I'm not sure if Paul meant to suggest to the contrary—he indicated that he would address whether "there was significant evidence that Officer Wilson's testimony was false" in a future post, which may or may not address this point—but I thought I would flag the issue in the meantime.

UPDATE: Paul has helpfully updated his post, and here's a reply: I agree that we would want the grand jury to assess probable cause including the possibility of self-defense. But there are strong reasons to be skeptical of a suspect's exculpatory claim to have acted in self-defense, just as there are reasons to be skeptical of a suspect's exculpatory claim on any other legal basis. All the grand jury is doing is making a probable cause determination, not "finding facts" in a trial sense, and there would be good reasons to discount a suspect's self-serving exculpatory testimony in arriving at the probable cause determination.