Mistake Defense in Wisconsin

An honest error, whether of law or of fact other than criminal law is a defense if it negatives the existence of a state of mind essential to the crime.  Crimes require a "mental state," for example, intentionally, recklessly, .... If a person's honest mistake makes it so the person lacked the required mental state, then the person is not guilty of the alleged crime.  The defense of mistake does not apply to the age of a minor. 

Mistake is not a defense to criminal negligence in Wisconsin.  A Wisconsin resident shoot a member of his deer hunting party thinking she was a deer.  The state charged him with felony negligently handling a weapon.  The defendant asked the judge at trial to insruct the jury regarding the mistake defense.  The judge refused to tell the jury about mistake.  The Wisconsin court of appeals agreed that the mistake was not a proper potential defense in the case.  The court of appeals held that: criminal intent is not relevant to whether he is guilty of negligent use of a dangerous weapon. Rather, the relevant inquiry is whether a reasonable person, under the same or similar circumstances, would realize that the conduct creates a substantial and unreasonable risk of death or great bodily harm. Because Lindvig's subjective state of mind is not essential to the crime of negligent operation of a dangerous weapon, he cannot assert the defense of mistake.