Mens rea
Federal criminal law

Since the federal government of the United States does not have a generalized police power like that of the states, the scope of its criminal statutes is necessarily circumscribed. Ordinary prosecutions are the province of the states, and only crimes connected to the constitutional powers may be pursued by the federal government. Nevertheless, the Supreme Court holds that required mens rea is an essential element of federal criminal offenses. Consequently, Title 18 of the United States Code does not use the aforementioned culpability scheme but relies instead on more traditional definitions of crimes taken from common law. For example, malice aforethought is used as a requirement for committing capital murder, and the Supreme Court has applied mental states such as "willfully."
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