I. Criminal liability and types of penalties
Criminal liability is generally made up of two elements: (1) the guilty act or omission known as the “actus reus”, and (2) the prohibited state of mind or guilty mind known as the “mens rea”.
Most criminal offences require the co-existence of the above two elements (i.e. actus reus and mens rea) at the same time. This concept is derived from the Latin expression “actus non facit reum nisi mens sit rea”, which means that "the act will not make a person guilty unless the mind is also guilty". For example, a person is not guilty of murder if he caused the death of another person by accidentally knocking him down with his car. The mens rea for the offence of murder requires an intention to kill another person or cause him very serious bodily injury, which is lacking in this example. However, this person may have committed the offence of dangerous driving causing death because the mens rea required in such an offence is an intention to drive the motor vehicle, which is present in this example. Whether this person is guilty of dangerous driving causing death depends on whether he committed the actus reus, i.e. whether he drove his car in a dangerous manner as defined in the legislation (see Question 4 under Case Illustration).
In some special cases, known as “strict liability offences”, no prohibited state of mind is required and a guilty act is sufficient for criminal liability. An example can be found in sections 8 and 10 of the Water Pollution Control Ordinance (Cap. 358). Under these sections, any person commits an offence if he discharges any polluting matter into the waters of Hong Kong in a water control zone. There is no need to prove that the offender knew of the existence of pollutants in the materials he discharged or that he intended to pollute the water.
It should also be noted that under the Hong Kong legal system, everyone is presumed innocent until the person has been proven guilty. Hence a person will only be treated as guilty of an offence if he or she is convicted by the Court. Upon conviction, that person will be sentenced (i.e. punished) by the Court (see Part A below).