Arizona Judges are told not to tell jurys about their powers of Nullification in item 41 at http://www.supreme.state.az.us/jury/power1.htm
41. Do not Instruct Juries on Jury Nullification; However, .... Except in extraordinary situations or where required by the Arizona Constitution, juries should not be instructed on the subject of jury nullification.
Jury Nullification allow the jury to vote free the accused when the law is unjust or unfair. It was often used in the past to free people accused of helping slaves escape.