The doctrine of jury nullification rests on two truths about the American criminal justice system: (1) Jurors can never be punished for the verdict they return, and (2) Defendants cannot be retried once a jury has found them not guilty, regardless of the jury's reasoning. So the juries in both the Rosenthal and Paey cases could have returned a "not guilty" verdict, even though Paey and Rosenthal were undoubtedly guilty of the charges against them.Balko relies on the excellent book on the súbject by Clay Conrad, Jury Nullification: The Evolution of a Doctrine. Conrad's book is the most important writing on the subject since Lysander Spooner's 1852 book, Trial by Jury (available on line here). I recommend both.
This may sound radical, perhaps even subversive, but jury nullification serves as an important safeguard against unjust laws, as well as against the unfair application of well-intended laws. It's also steeped in American and British legal tradition.
(Hat tip to Glenn Reynolds who also links to his review of Conrad's book)
Update: Clay Conrad has a blog about juries called jurygeek. The reason I recommend his book so highly is that he is very sensitive to the variations on what jury nullification might mean, how it worked historically, the past and present legal treatment of it, and the practical implications of explicitly allowing it.