10. In which of the following situations would the defendant's mistake most likely constitute a defense to the crime charged?

Mistake of law is almost never a defense to a crime. Lacking knowledge that an act constitutes a crime, even if the lack of knowledge is reasonable, is not a defense to that crime.

Mistake of fact is available as a defense only if it negates a requisite intent element (i.e., mens rea) for the crime. Specific intent requires the defendant to have a specific intent or objective to commit the crime. For a specific intent crime, any mistake of fact is a defense. Specific intent crimes include assault as an attempted battery.

On the other hand, general intent crimes require that the defendant be aware of his actions and any attendant circumstances. General intent may be inferred from the act itself. For a general intent crime, only a reasonable mistake of fact is a defense. Examples of general intent crimes include assault as a threat.

Strict liability crimes require only that the underlying crime be committed, and do not require a mental element at the time the crime was committed. For a strict liability crime (one where no intent, or mens rea, is required), mistake of fact is never a defense. Illegal sale of alcoholic beverages, for example, is a strict liability crime.

B is correct. The question asks in what situation would the defendant's mistake most likely constitute a defense to the crime charged. The crime of assault exists where either: (i) the defendant attempts to commit a battery and fails; or (ii) the defendant intentionally places another in fear of imminent injury. Here, the defendant was unaware that the person who grabbed him was a police officer, and, so, the defendant's mistake as to the identity of the person grabbing him would negate his intent to commit a criminal unlawful touching of another. The defendant could not be said to have had the intent to commit a battery because he did not believe that his use of force was unlawful; he believed it was in self-defense. The defendant mistook the identity of the police officer; he did not intend to commit an unlawful offensive touching of another.

A is incorrect. Here, the crime charged is the illegal sale of alcohol, a strict liability offense. As discussed above, for a strict liability crime (one where no intent, or mens rea, is required), mistake of fact is never a defense. As such, the defendant's mistake here does not negate the mental state necessary for the offense because the crime charged does not require the defendant to have intended to commit the crime. In other words, the defendant need not have intended to sell to an underage person to be convicted of the offense. As such, his mistake as to the age of the person is not a valid defense.

C is incorrect. Here, the crime charged is statutory rape, a strict liability offense. Strict liability crimes require only the underlying crime be committed (in this case, intent to have sex with a person who is underage), and do not require a mental element at the time the crime was committed (in this case, criminal liability does not hinge on whether the defendant knew the person was underage). The defendant's mistake in thinking the prostitute was 18 years-old does not negate the mental state necessary for the offense because the crime charged does not require the defendant to have intended to commit the crime. In other words, the defendant need not have intended to have sex with a person under the age of 18 to be convicted of the offense. Accordingly, the defendant's mistake as to the age of the person is not a valid defense.

D is incorrect. Mistake of law is almost never a defense and lacking awareness or knowledge that an act constitutes a crime, even if the lack of knowledge is reasonable, is not a defense to that crime. The only exceptions where mistake of law may be a defense are when there is reasonable reliance on an invalid statute or the crime itself requires knowledge of the law. Here, however, neither of these situations apply and mistake of law, based on reliance on an attorney, will not be a basis for the defendant's defense.