A bill of attainder (also known as an act of attainder or writ of attainder) is an act of a legislature declaring a person or group of persons guilty of some crime and punishing them without benefit of a judicial trial.
Bills of attainder were used through the 18th century in England, and were applied to British colonies as well. One of the motivations for the American Revolution was anger at the injustice of attainder—though the Americans themselves used bills of attainder to confiscate the property of British loyalists (called Tories) during the revolution. American dissatisfaction with attainder laws motivated their prohibition in the Constitution (see the case of Parker Wickham).
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