What does ACTNS NON FACIT REUM, NISI MENS SIT REA mean?

ACTNS NON FACIT REUM, NISI MENS SIT REA meaning in Law Dictionary

n work doesn't make [the doer from it] responsible, unless your head be bad; that is, unless the objective be unlawful. 3 Inst. 107. The intention therefore the act must both concur to constitute the criminal activity. Lord Kenyon, C. J., 7 Term 514; Broom, Maximum. 300.