Every DNA reversal is a lesson in the problems with one prosecutorial tool or another. Witnesses are unreliable. Criminals will lie in exchange for lenient treatment. Mr. Lloyd's case shows that even a signed confession is not always what it seems. And it provides further proof that the American justice system is imperfect at best, and frequently far too flawed to rely on capital punishment. In 1985 Mr. Lloyd's judge decried Michigan's lack of a death penalty, but its absence now appears to be all that prevented him from sentencing an innocent man to die.