Basic principles of criminal law

Contributed by Marcus Hassall, Blackburn Chambers and current to March 2022.

There are four major principles of the criminal law system:

1. a person is presumed innocent until proven guilty;
2. a person’s guilt must be proven “beyond reasonable doubt”;
3. no person can be required to incriminate himself or herself; and
4. a person who has been acquitted cannot be tried again for the same offence.

As set out below, some of the above principles have been modified or eroded by recent developments.

The presumption of innocence

A fundamental principle of our criminal justice system, sometimes called “the golden thread”, is that a person is presumed innocent until proven guilty. In other words, it is up to the prosecution to prove an accused’s guilt. Ordinarily, an accused person does not have to prove anything, and in particular there is no burden on the accused to prove his or her innocence. In the ACT this principle is enshrined in s 22, Human Rights Act 2004.

Proof beyond reasonable doubt

Another key principle in Australia is that, in a criminal case, the prosecution must prove a person’s guilt “beyond reasonable doubt”. This is a high standard of proof, particularly compared to civil cases, where the standard is “the balance of probabilities”.

The prosecution must prove every element of the alleged offence by the accused beyond reasonable doubt – for example, not only that the accused did the prohibited act, but that he or she did so with criminal intent.

There are some situations where, if the accused wants to defend the case in a particular way, he or she will have to show that there is at least some evidence to support a particular defence (such as self-defence), or alternatively will have to prove a particular defence on the balance of probabilities (e.g. insanity). Even in these situations, however, it will still be up to the prosecution to prove the other aspects of the case "beyond reasonable doubt".

The privilege against self-incrimination

It is a general principle of the criminal law that a person is not required to answer questions put by a police officer or other official investigating a criminal offence. The effect of the principle is that, ordinarily, a person is entitled to say nothing at all, and remain silent.

The “privilege against self-incrimination” is subject to exceptions – for example, the driver of a motor vehicle must produce his or her licence when asked to do so by police.

In some jurisdictions (e.g. NSW), if a suspect remains silent during police questioning, and at trial seeks to rely on something which he or she could have mentioned during the questioning, the court may be permitted to draw an adverse inference against the accused. That is not the law, however, in the ACT, where there is no legal obligation on an accused to say anything at all during police questioning.

The rule against double jeopardy

The rule against double jeopardy means that, ordinarily, once a person has been tried and acquitted of an offence, he or she cannot be charged again with the same offence. Some of the aims of this rule are to create finality, and to prevent abuses of government power.

In 2016, however, the ACT Parliament passed legislation abolishing the rule against double jeopardy in cases where:

• After a person is acquitted of a “Category A offence” (i.e. an offence punishable by imprisonment for life such as murder, large commercial supply of narcotics), “fresh and compelling evidence” emerges of the person’s guilt; and
• A person’s acquittal of a “Category B offence” (i.e. an offence punishable by imprisonment for 15 years or more) was tainted by perjury, false evidence, corruption or some other “administration of justice offence”.

Even in these cases, the re-trial of a person previously acquitted can only proceed if the ACT Supreme Court is satisfied that the re-trial is “in the interests of justice”.

A number of other Australian States and Territories have introduced similar legislation (i.e. abolishing the rule against double jeopardy in restricted cases).