Autrefois acquit

n. claim that the accused has already been acquitted and therefore may not tried again for the same offense

In the common law, the peremptory pleas (pleas in bar), are pleas that set out special reasons for which a trial cannot go ahead. They are the plea of autrefois convict, the plea of autrefois acquit, and the plea of pardon.A plea of autrefois convict (Law French for "previously convicted") is one in which the defendant claims to have been previously convicted for the same offence and that hence they cannot be tried again. A plea of autrefois convict can be combined with a plea of not guilty.A plea of autrefois acquit (Law French for "previously acquitted") means the defendant claims to have been previously acquitted of the same offence, on substantially the same evidence, and that hence he or she cannot be tried again. A plea of autrefois acquit can be combined with a plea of not guilty.
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autrefois acquit, claim that the accused has already been acquitted and therefore may not tried again for the same offense

Previously acquitted; an accused cannot be tried for a crime because the record shows he has already been subjected to trial for the same conduct and was acquitted. - (read more on Autrefois acquit)