Prior bad acts are sometimes allowed as evidence in a criminal case as proof of motive, opportunity, intent, preparation, plan, knowledge, identity, or absence of mistake or accident. They are governed by federal and state evidence rules, which vary by state. Becuase of the potential for prejudice to the defendant, they must be substantially relevant for some purpose other than to point out the defendant's criminal character and thus to show the probability that he acted in conformity therewith. Therfore, the relevance and probative value of the evidence must be demonstrated.
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