The terms actus reus and mens rea developed in English Law are derived from a principle stated by Edward Coke, namely, actus non facit reum nisi mens sit rea,[1] which means: "an act does not make a person guilty unless (their) mind is also guilty"; hence, the general test of guilt is one that requires proof of fault, culpability or blameworthiness both in thought and action.
Commentator Dennis Baker asserts: Although lawyers find the expression actus reus convenient, it is misleading in one respect.
In English law, there is no Good Samaritan rule therefore one cannot be criminally liable for an omission unless a duty of care is owed.
Some countries like the United States have avoided the common law conclusion in Regina v. Dugdale[9] by legally defining possession as a voluntary act.
[14] Decina argued, inter alia, that he had not engaged in criminal conduct because he did not voluntarily strike the school girls.
[15] The New York Court of Appeals disagreed and held that since the defendant knew he was susceptible to a seizure at any time without warning and decided to operate a motor vehicle on a public highway anyway, he was guilty of the offense.
"To hold otherwise," wrote Froessel, J, "would be to say that a man may freely indulge himself in liquor in the same hope that it will not affect his driving, and if it later develops that ensuing intoxication causes dangerous and reckless driving resulting in death, his unconsciousness or involuntariness at that time would relieve him from prosecution[.
]"[16] In Hill v Baxter, Kilmuir, LC, articulated the necessity of eliminating automatism, defined as "the existence in any person of behaviour of which he is unaware and over which he has no conscious control,"[17] in proving the voluntariness of the actus reus: [N]ormally the presumption of mental capacity is sufficient to prove that he acted consciously and voluntarily and the prosecution need go no further.
But, if after considering evidence properly left them by the judge, the jury are left in real doubt whether or not the accused acted in a state of automatism...they should acquit because the necessary mens rea—if indeed the actus reus—has not been proved beyond a reasonable doubt.Thus, a person suffering from somnambulism, a fugue, a metabolic disorder, epilepsy, or other convulsive or reflexive disorder,[18] who kills another, steals another's property, or engages in other facially criminal conduct, may not have committed an actus reus, for such conduct may have been elicited unconsciously, and "one who engages in what would otherwise be criminal conduct is not guilty of a crime if he does so in a state of unconsciousness[.
[20] While the general scientific consensus is that hypnosis cannot induce individuals to engage in conduct in which they would not otherwise engage,[21] the Model Penal Code, as well as the criminal codes of Montana, New York, and Kentucky do provide hypnosis and hypnotic suggestion as negating volition, and consequently, actus reus.
[24] The Supreme Court of Canada ruled confessions made under hypnosis inadmissible because they are involuntarily given; Germany and Denmark provide a hypnotist defense.