[Hodar]

Mens rea is Latin for "guilty mind".[1] In criminal law, it is viewed as one of the necessary elements of a crime. The standard common law test of criminal liability is usually expressed in the Latin phrase, actus non facit reum nisi mens sit rea, which means "the act does not make a person guilty unless the mind is also guilty". Thus, in jurisdictions with due process, there must be an actus reus accompanied by some level of mens rea to constitute the crime with which the defendant is charged (see the technical requirement of concurrence). As a general rule, criminal liability does not attach to a person who acted with the absence of mental fault. The exception is strict liability crimes.

Source

Since she told him she was 19, it is reasonable for him to believe he was not committing a criminal act. Case closed.

[massmike]

Since she told him she was 19, it is reasonable for him to believe he was not committing a criminal act. Case closed.

That won't work for the bartender! I've seen bars and liquor stores closed down for selling to someone with a phony ID.