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The defendant cannot be forced to give evidence and can choose whether to do so or not. A defendant who decides to give evidence does so by going into the witness box, taking the oath (or affirming) and answering any questions asked first by the defendant's lawyer and then by the prosecutor in cross-examination. The defendant may also call witnesses who are able to give evidence relevant to the defence.

There are a number of different defences available to a defendant and common defences are discussed below.

If appropriate, a defendant may rely on more than one defence as alternative defences, but must be careful not to prejudice a good defence by throwing in weaker or conflicting ones.

Reasonable Doubt

In addition to other defences the defendant may attempt to raise doubts in the prosecution case.

The defence will attempt to demonstrate any inconsistencies and shortcomings in the prosecution case.

Where all the elements which make up the offence are not proved beyond reasonable doubt on the evidence presented, the defence is entitled to submit that the prosecution has not proved its case. If this is accepted the defendant will be found not guilty.


For details about the criminal responsibility of children, see CHILDREN AND YOUNG PEOPLE, Young Offenders, Criminal responsibility.


An alibi is used to show that the defendant could not have committed the crime because she or he was not at the scene of the crime when the offence was alleged to have been committed, but rather, was somewhere else.

This evidence may be given by the defendant and by other witnesses on the defendant's behalf.

Under s 124 of the Criminal Procedure Act 1921 (SA) if a defendant proposes to introduce evidence of alibi at the trial of an indictable offence in the Supreme Court or the District Court prior notice of the proposed evidence must be given, which is filed at the same time as the defence case statement is filed. This is not required if the essentially the same evidence was given at the preliminary examination where the defendant was committed to trial [s 124(3)].


In cases of assault and sexual assault it may be a defence that the person complaining of being assaulted gave consent (free and voluntary agreement ) to the alleged assault. For example, in many sports, where players anticipate and agree to a certain level of contact.

This is a particularly difficult area of the law - please see further descriptions of the law in this area in our sections on Rape and Indecent Assault.

There are some people who cannot legally consent, for example children (see in particular the handbook sections on child sexual assault, and unlawful sexual intercourse). Another example is where there is undue influence on people with a cognitive impairment (see further the handbook section on Sexual offences where the victim has a cognitive impairment (for example an intellectual disability).

Defence of property

Under s 15A of the Criminal Law Consolidation Act 1935 (SA) a person is entitled to use such conduct as he or she genuinely believes is necessary and reasonable to defend property from being taken, destroyed, damaged or interfered with; to prevent criminal trespass; to remove a trespasser; or to arrest someone unlawfully at large - as long as the conduct was reasonably proportionate to the threat the defendant genuinely believed to exist, and if the conduct resulted in death, the defendant did not act recklessly or intend to cause death.

However, see also: Home invasion where the requirement of reasonable proportionality does not apply.

It is a partial defence to a charge of murder (reducing the offence to manslaughter) in some circumstances [s 15A(2)].

Criminal trespass in relation to this defence is where someone comes on to a property with the intention of committing an offence (against the person or property) [s 15A(3)].

If a defendant raises this defence then it is for the prosecution to disprove it beyond reasonable doubt [s 15A(4)].

Home invasion

In the case of a home invasion (that is, a serious criminal trespass in a place of residence), acting for a defensive purpose or to defend property can be complete defences to an offence, including murder, even if the defendant's conduct was not objectively reasonably proportionate to the perceived threat [s15C Criminal Law Consolidation Act 1935 (SA)].

What is required is that the defendant genuinely believed that the victim was committing or had just committed a home invasion [s 15C(2)(a)].

This section is not available if the victim was an on-duty police officer [s 15C(1)(b)], or if the defendant was themselves engaged in criminal activity that might have given rise to the threat [s 15C(2)(b)], or if the defendant was affected by drugs (unless involuntarily taken, or prescribed or over-the-counter and used appropriately [s 15C(2)(c)].


A defendant may raise the defence of duress where the immediate threat of death or serious personal violence was so great that it overcame the defendant's resistance to carrying out the criminal act. There is a subjective and objective test involved in assessing this defence.

Duress cannot be a defence to murder [ R v Howe [1987] AC 653].

Necessity (duress of circumstance)

This defence is available where an accused believes, on reasonable grounds, that commission of the crime charged was necessary in all the circumstancesin order to remove an imminentthreat of death or serious injury to themselves or another. The response must be proportionate to the danger and there are both subjective and objective considerations when assessing this defence [see: Bayley v Police (2007) 99 SASR 413].

The defence of necessity is approached by courts with considerable caution.


It is not generally a defence to have been intoxicated by alcohol or drugs at the time of committing an offence. However, Part 8 of the Criminal Law Consolidation Act 1935 (SA) [ ss 267A - 269] provides an intoxication defence in limited circumstances.

This defence is based on the argument the defendant’s consciousness was (or may have been) impaired to the point of criminal irresponsibility at the time of the offence.

Intoxication is not a defence when the defendant formed an intention to commit the offence before becoming intoxicated or where the defendant became intoxicated for resolve to commit the offence. Intoxication is generally not a defence when the intoxication is self induced.

Recreational use of a drug is considered self induced use. Where intoxication arose from both recreational use and therapeutic use of drugs (or the same drug) the resulting intoxication is also considered self induced.

Evidence of intoxication can also be damaging to a defendant’s case. It can form the basis for an inference of intent or motive and can also establish criminal negligence. Whilst intoxication can be viewed as a mitigating factor at sentence, it is more often viewed as an aggravating factor, resulting in an increase in penalty when the defendant is sentenced.

This is a complicated defence and should not be used without proper legal advice and representation.

Mental Impairment

The Criminal Law Consolidation (Mental Impairment) Amendment Act 2017 (SA) has changed this area of the law substantially to:

  • limit cases where mental incompetence has been caused by self-induced intoxication
  • ensure the paramount consideration when determining whether to release a defendant on licence, is the safety of the community
  • enable matters to be dealt with through fewer reports,
  • provide more options for dealing with less serious, summary and minor indictable, matters.

Section 269C of the Criminal Law Consolidation Act 1935 (SA) outlines a general defence of Mental Impairment, where because of a mental illness, intellectual disability or a disability or impairment of the mind resulting from senility, the defendant did not know the nature and quality of their conduct or could not reason that what they did was wrong or were totally unable to control their conduct.

The law recognises that such persons do not have the mental element of a guilty mind that is required to be found guilty of a criminal offence.

Sub-section 269C(2) sets out that where a person is found to be mentally incompetent to have committed the offence, but the trial judge is satisfied, on the balance of probabilities, that the mental impairment was substantially caused by self-induced intoxication, the person may be dealt with instead under Part 8, see Intoxication. Sub-sections 269A(2a) and (2b) states that intoxication resulting from recreational use of drugs or the combined effect of therapeutic and recreational use is to be regarded as self-induced. Sub-section 269C(3), however, does allow for the court to make an order that a person whose mental impairment was substantially caused by self-induced intoxication still be dealt with under the mental impairment provisions of Part 8A of the Act [see s 269C(3)]. The court can make such an order where it is in the interests of justice to do so, and taking into account whether the making of such an order would affect public confidence in the administration of justice [s 269C(3)].

There is a presumption of mental competence [s 269D] and to make use of the mental impairment defence, mental incompetence must be shown on the balance of probabilities. The possible consequences of a finding of mental impairment are unconditional release or release on strict conditions of supervised licence or detention in secure psychiatric care [ss 269NB and 269O]. It is a condition of every licence for release that the defendant be prohibited from possessing firearms and ammunition. The Court may also direct a defendant to surrender a firearm [ss 269NC and 269OA]. When determining whether to release a defendant, either unconditionally or on a licence, the paramount consideration must be the safety of the community [ss 269NA and 269NI].


Provocation is not a defence to a charge of assault. It can only be used as a defence to reduce a charge from murder to manslaughter (it is not a complete defence). In any other case it cannot be used as a defence although, after conviction, it can be taken into account by the court when considering an appropriate penalty.

The provocation defence is only available where the defendant hears first hand of the thing that provokes them.

This is where a person in the defendant's situation, and who has the defendant's characteristics, but possessed of ordinary self control, would be so affected by the victim's words and actions as to lose self-control as the defendant did.

The provocation has to have actually caused the loss of self-control and act as the defendant did, and it is not merely an act of vengence.

The gravity of the provocation has to be assessed by reference to the relevant characteristics of the accused and then the question is whether the provocation of that gravity would have caused the ordinary person to lose self-control (viewed objectively and without the characteristics of the accused except maturity and age) [See : R v Lindsay (2014) 119 SASR 320].

Self defence

A person is entitled to use such conduct as he or she genuinely believes is reasonable and necessary for a 'defensive purpose' (that is, in self-defence or in defence of another, or to prevent or end an unlawful imprisonment) under s 15 Criminal Law Consolidation Act 1935 (SA).

If a defendant raises a defence under this section, the defence is taken to have been established unless the prosecution disproves the defence beyond reasonable doubt.

This will be a complete defence to an offence, including murder, as long as the force used was, in the circumstances as the defendant genuinely believed them to be, reasonably proportionate to the threat the defendant genuinely believed to exist (for example, see Zecevic v DPP (1987) 162 CLR 645). See however the exception to reasonable proportionality in: Home invasion.

It will be a partial defence to murder, reducing the offence to manslaughter, if, despite the defendant believing his or her actions were necessary, the conduct was not reasonably proportionate to the threat that the defendant believed existed.

    Defences  :  Last Revised: Mon Sep 28th 2015
    The content of the Law Handbook is made available as a public service for information purposes only and should not be relied upon as a substitute for legal advice. See Disclaimer for details. For free and confidential legal advice in South Australia call 1300 366 424.