Section 79

Unless otherwise provided by written law, nothing is an offence which is done by any person who by reason of a mistake of fact or in ignorance of a fact in good faith believes himself to be bound by law to do it or justified by law in doing it.

Despite subsection (1), when a mistake of fact or ignorance of a fact negates the fault element required to establish liability under an offence, then to avoid doubt, that offence is not made out. Explanation.—Where the physical and fault elements of an offence are proven, and the accused person proves the defence under subsection (1), the accused person is not guilty of that offence.Illustrations (a) A sees Z commit what appears to A to be a murder. A, in the exercise, to the best of his judgment exerted in good faith, of the power which the law gives to all persons of apprehending murderers in the act, seizes Z, in order to bring Z before the proper authorities. A has committed no offence, though it may turn out that Z was acting in self-defence. (b) A, a police officer, is deployed to perform the duty of screening passengers boarding a flight at the airport. A sees Z, a passenger queuing up to be screened, acting suspiciously. As A approaches Z, Z suddenly shouts aloud that he is carrying a bomb and warns A not to approach further. As A draws his revolver, Z suddenly starts to run away. A, after assessing the circumstances of the case, and to the best of his judgment exerted in good faith, believes that Z has a bomb and will set it off. A shoots Z and Z dies as a result. A has committed no offence, even though it may turn out that Z was not carrying a bomb. (c) A, a police officer, is deployed to perform patrol duty at an underground train station. A receives information from police headquarters that someone is attempting to plant a bomb in the public transport system. The profile of the suspect is also provided. While patrolling the underground train station, A sees Z, who fits the profile. Z is seen carrying a backpack and behaving suspiciously. A approaches Z and orders him to stop. Z suddenly starts running towards a crowd in the station. A, after assessing the circumstances of the case, and to the best of his judgment exerted in good faith, believes that Z has a bomb and will set it off. A shoots Z and Z dies as a result. A has committed no offence, even though it may turn out that Z was not carrying a bomb. (d) X, the commander of a naval vessel, is patrolling Singapore territorial waters. X receives information that someone may hijack a vessel in order to commit a terrorist act. X spots vessel A which is proceeding at high speed towards a cruise liner. X orders vessel A to stop her manoeuvre immediately and fires a warning signal. Vessel A instead starts accelerating towards the cruise liner. X, after assessing the circumstances of the case, and to the best of his judgment exerted in good faith, believes that vessel A is going to ram into the cruise liner. X gives an order to fire at vessel A. The persons on board vessel A die as a result. X has committed no offence, even though it may turn out that vessel A was not hijacked nor were there any terrorist on board. (e) A, an officer of a court, being ordered by that court to arrest Y, and, after due enquiry, believing Z to be Y, arrests Z. A has committed no offence. (f) A sees a watch on Z’s desk, which is identical to one that A owns, and mistakenly believes the watch is actually his. A intentionally takes the watch out of Z’s possession without Z’s consent while labouring under such mistaken belief. A has not committed an offence of theft as he did not intend to dishonestly take the watch out of Z’s possession.