The debacle of missing files in the Timothy McVeigh case has suddenly turned the public's eye on the rule that prosecutors must disclose exculpatory evidence to the defense. The circumstances of the McVeigh case are unusual and suggest no bad faith by the prosecutors. But the risk, though very small, that a man facing execution could win a new trial raises the question why this rule has proved so hard to follow.
Prosecutors are only human and what's worse, they're lawyers.
Years of pitched courtroom battles have honed their natural desire to win. So when the Supreme Court says they have to turn over any evidence that might help the other side, their strongest instincts rebel. The real difficulty with the disclosure rule is that it is almost impossible for prosecutors in the heat of a case to know exactly what the rule requires them to disclose. Even an honest prosecutor will have a hard time deciding which evidence truly casts doubt on guilt. When a prosecutor is personally convinced the defendant is guilty, it can take enormous self-discipline to turn over evidence she thinks is meaningless when she knows the defense could use that evidence to plant doubt in jurors' minds.