Intent is an element of wire fraud, mail fraud, bankruptcy fraud, etc. that the Government is required to prove beyond a reasonable doubt. So the technical answer to your question is, no it is not a defense. The affirmative burden to prove intent lies on the Government.
I agree with my colleagues but in practice the intent may be inferred from your actions. If the case is in US District Court for the Central District of California - the rulings of the 9th Circuit Court of Appeals will control if applicable.
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As you may known "scienter" just means knowledge. Sometimes the term is used loosely as equivalent to "mens rea," which means guilty mind, but I think it is better to distinguish the concept of scienter from other terms relating to what is going on in someone's mind. In federal fraud cases--whether brought under Section 1341, 1343, or 1344 of Title 18--the government must prove that you knowingly and intentionally attempted to or carry out a scheme or artifice to defraud another person of money or other things of value using false and fraudulent representations . To defend against such a charge, one may argue that he did not so intend. In the strict sense, I suppose, a scienter defense would consist in denying that you knew that the representations allegedly made were false. The Ninth Circuit and the United States Supreme Court have decided a number of cases explaining good faith as a defense in fraud cases.
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