In Australia, individuals charged with a criminal offence may rely on a range of legal and factual defences. A criminal defence is an argument or justification that explains why an individual committed a particular offence. These defences are typically divided into two main categories: complete defences and partial defences.
Complete Defences
A complete defence, if accepted by the court, results in complete exoneration from any criminal liability. This means the accused will be found ‘not guilty’ of the charges. Some complete defences are specific to certain offences and are laid out in corresponding legislative instruments; however, most originate in common law.
Mistake of Fact
The defence of mistake of fact requires demonstrating that:
- You held a mistaken belief or were ignorant of the facts or circumstances surrounding an act or omission.
- Due to this mistaken belief, you did not possess the ‘mental element’ required to commit the offence.
- Had the facts been as you reasonably believed at the time, no criminal offence would have been committed.
- The belief you held was honest and reasonable in the given circumstances.
It’s crucial to note that this defence applies only to mistakes of fact, not law; ignorance of relevant laws in your jurisdiction does not constitute a criminal defence.
Example: Kylie arrives at Sydney Airport from New Zealand and waits at the corresponding baggage carousel for her checked baggage to emerge. When a pink Barbie bag identical to hers appears, she takes it, believing it to be hers. Once home, she discovers it’s not her bag. In this situation, Kylie’s honest and reasonable belief that she was collecting her own bag could support a defence of mistake of fact.
Claim of Right
A claim of right defence can be raised when an individual is recovering property or money they believe belongs to them or someone else. This defence isn’t limited to the specific item previously held by the person attempting recovery but can extend to property of equal value. Moreover, it’s available to a person acting on behalf of another whom they believe has an honest claim to that property.
It should be noted, however, that although this defence may apply, a person cannot commit further criminal acts (e.g., assault or trespass) while attempting to recover property.
Consent
The latin maxim volenti non fit injuria — “no injury is done to one who consents” — underlies the common law defence of consent, defined as giving permission or agreement for an action to occur. While consent is a well-established legal principle, it applies to a limited range of offences. Certain crimes, such as incest, sexual offences with minors, slavery, female genital mutilation, and bestiality, do not permit consent as a defence.
In situations where consent is available as a defence, the lack of consent can turn otherwise lawful acts into criminal offences. Examples include:
- Sexual intercourse becoming the offence of rape,
- Sparring or boxing becoming assault,
- Surgery becoming wounding,
- Taking property becoming stealing,
- Abortion or euthanasia becoming murder,
- Mural paintings becoming damaging property,
- Entering another’s property becoming trespass.
Necessity
Also referred to as ‘sudden or extraordinary emergency’, the defence of necessity applies when an unlawful act is committed to respond to an immediate, significant threat. For this defence to succeed, the court assesses whether the unlawful act was the only reasonable way to address the emergency and whether the response was proportionate given the circumstances.
Duress and Coercion
The defence of duress protects a person from criminal liability if the offence was committed to avoid serious, imminent harm to themselves or others. When invoking duress, the court considers whether:
- The accused faced genuine imminent threats of death or serious injury to themselves, a family member, or another person,
- A reasonable person would have acted similarly in response to the threat,
- The accused had no other lawful means to counter the threat.
If these conditions are met, duress may be a valid defence. If any condition fails, the defence of duress is unavailable.
Self-Defence
Self-defence absolves an individual of criminal responsibility when force is used to protect oneself or others, as long as the force is necessary and reasonable in response to an imminent, perceived threat. The threat does not need to have materialised; one may act pre-emptively in anticipation of the imminent threat. This defence is applicable when the force used is minimal and proportionate to the perceived level of threat.
In cases where self-defence leads to death, section 421 of the Crimes Act 1900 provides that excessive force may reduce a murder charge to manslaughter. Section 419 of the Crimes Act 1900 specifies that, once raised, the burden shifts to the prosecution to disprove the defence.
Intoxication
Historically, self-intoxication served as a common law defence until the late 1900s, but most Australian states and territories have since enacted legislative provisions addressing intoxication. In New South Wales, Part 11A of the Crimes Act 1900 provides that, for specific intent offences, intoxication may be considered if the intent was formed during and as a result of the intoxication. However, this defence will not succeed if the intent to commit the offence was established prior to becoming intoxicated. If this defence is successfully argued for a specific intent offence, the individual would instead be convicted of a less serious offence.
Mental Illness
The mental illness defence applies when a person has such a severe mental illness or cognitive impairment that they cannot be held fully responsible for their actions, making punishment inappropriate. This is due to the loss of deterrence and retribution as justifiable purposes of punishment.
For most offences, mental illness acts as a complete defence. Section 23A of the Crimes Act 1900 states that in cases where mental impairment would otherwise result in a murder conviction, the charge is instead reduced to manslaughter. Proving this defence requires evidence of significant cognitive and emotional impairments, such as the inability to distinguish between right and wrong and impaired self-control.
Automatism
Automatism, or involuntary actions performed without conscious volition, can act as a defence if the offence occurred as a result of involuntary movements. Examples include muscle spasms, involuntary jerking, or sleepwalking, often due to medical conditions like sleeping disorders, epilepsy or an extreme stress responses.
Partial Defences
A partial defence reduces the charge rather than eliminating liability entirely. In New South Wales, partial defences are available only in murder cases, potentially reducing a murder charge to manslaughter.
Extreme Provocation
Under section 23 of the Crimes Act 1900, extreme provocation may serve as a partial defence for murder, leading to a manslaughter conviction if the accused’s response to provocation was so extreme it would deprive a reasonable person of self-control, resulting in an intention to kill or cause grievous bodily harm.
Diminished Responsibility
Mental abnormalities can sometimes serve as a partial defence to murder, reducing the offence to manslaughter under section 23A of the Crimes Act 1900. This defence is inapplicable if impairment was caused by self-induced intoxication. Proving diminished responsibility involves showing:
- The accused was affected by an abnormality of mind,
- This abnormality arose from developmental issues, disease, or injury, and
- The abnormality significantly impaired their mental responsibility for the offence.
If all criteria are met, diminished responsibility may be accepted as a defence.