Doubting Prosecutors

So you're a prosecutor. Your boss, the district attorney, asks you to prosecute a case in which you strongly believe the defendants are innocent. What do you do?  Assume that the DA's decision to prosecute is based on a good-faith belief in the defendant's guilt, and there's no evidence of evidence hiding or other extra-legal malfeasance.

I'm not sure that this guy's approach was the correct one, but it sure makes for a fascinating story (for those of you who don't want to click through and read—he took the case, then surreptitiously helped the defense lawyers—and deliberately lost the case in court).

But I'm not sure what the correct course of action should be, either. I'm tempted to say you resign in protest, then tell the defense team what you know. But what if sticking around for a bit longer could help you get access to more information confirming the defendants' innocence—information that would likely be left undiscovered were you to resign?

Discuss.