When you are charged with an offence by the police, they are required to be able to prove that charge "beyond reasonable doubt".
Under the common law tradition, it is not the responsibility of the accused person to prove his or her innocence; in other words, " the onus of proof" never rests with the defence.
Rather, the prosecution is required to prove all elements (or ingredients) of the alleged offence to a standard of proof known as beyond any reasonable doubt.
The defendant, on the other hand, is presumed to be innocent until and unless the prosecution is able to discharge its onus of proving guilt beyond reasonable doubt in a court of law.
So, what does all this mean?
What is a standard of proof?
The standard of proof is the degree to which a decision-maker is convinced that an offence has occurred; a decision-maker including a magistrate in the Local Court, or a jury or judge-alone (in judge-alone trials or cases) in a higher court such as the District or Supreme Court.
In civil law matters, which include cases where individuals or companies commence proceedings against others for damages, compensation and the like, the standard of proof is "on the balance of probabilities".
This means the decision-maker must be convinced it is more likely than not that the person making the claim – such as the applicant or plaintiff – has established its case.
Expressed in another way, it means the case has been established by more than 50%.
This civil law standard of proof is embodied in section 140 of the Evidence Act 1995 (NSW).
Criminal cases are where the state prosecutes an individual or company for a criminal offence, such as an assault, drug offence, theft or the like.
In these cases, the standard of proof is beyond reasonable doubt.
This standard is higher than the civil law standard of proof as it is an attempt to both rectify the unequal power imbalance between the state and an individual as well to reflect the seriousness of the consequent loss of liberty if found guilty (as opposed to mere monetary cost in civil cases).
But the courts have made clear that phrase 'beyond reasonable doubt' is to be understood only by its ordinary meaning, not by any codified test, whether based on separate criteria or not.
The Honourable Justice Newman in the Court of Criminal Appeal case R v GWB  NSWCCA 410 said at  that:
"judges should not depart from the time honoured formula that the words 'beyond reasonable doubt' are words in the ordinary English usage and mean exactly what they say".
Although the prosecution must always prove each element of their case beyond reasonable doubt, the defendant might make a positive case in their defence – that what is alleged happened differently or had a legal justification, for instance that an act of violence was in self-defence.
If the defence raise a case they must prove, it is to the lower standard of on the balance of probabilities.
These criminal law standard of proof is embodied in section 141 of the Evidence Act 1995 (NSW).
Where does the standard of proof come from?
Our legal system is based on the presumption of innocence.
Again, this means that a person accused of a crime is presumed to be innocent of that crime until and unless that person is found guilty in a court of law.
This presumption has become an essential part of our system of justice to ensure fairness.
Roman law had the maxim ei incumbit probatio qui dicit, non qui negat or "proof lies on him who says, not on him who denies".
The concept also can be found in the traditions of Jewish and Islamic religious laws. This concept was brought into the English common law in the early Renaissance through influence from the Catholic Church and its canon law, which is based on the ancient Roman system.
In 1791, the concept was pithily phrased by the barrister Sir William Garrow as "presumed innocent until proven guilty". This statement ties together the two key legal concepts of the presumption of innocence and the burden of proof; accordingly it has since become known as the ' golden thread'.
William Blackstone writing on English laws a generation before Garrow stated the philosophy that underpins both the presumption of innocence and the burden of proof being beyond reasonable doubt: "It is better that ten guilty persons escape than that one innocent suffer."
The United Nations has also enshrined the importance of the presumption of innocence and burden of proof in international law under Article 14 of the International Covenant on Civil and Political Rights.
Who decides if a charge has been proven beyond reasonable doubt?
In criminal law cases, most matters are resolved in the Local Court, which is termed "summary prosecution" in legal lingo.
The Local Court is presided over by a Magistrate, who is a local court judicial decision maker. This is an independent legal professional who oversees local court matters at all stages, from beginning to end. In cases being decided by the local court at hearing, the Magistrate is the decision-maker for both questions of fact and questions of law.
More serious cases are dealt with "on indictment", which escalates the matter to the District Court and entitles the defendant to a trial by jury.
A jury trial means that the jury are the decision-makers for questions of fact, while questions of law are decided by a District Court Judge.
However, in certain cases a defendant can forego their right to a jury in favour of a judge-alone trial, where the judge is decision-maker for both questions of fact and questions of law, like a Local Court Magistrate.
The most serious cases the indictment is dealt with in the Supreme Court, in a trial by jury overseen by a Justice of the Supreme Court. Similarly, in certain circumstances a defendant can forego a jury in favour a judge-only trial presided over by a Supreme Court Justice.
So, this decision as to whether a charge has been proven beyond reasonable doubt is a matter for a magistrate, a judge, or jury members to decide depending on the case.
Can an innocent person be found guilty?
Deciding whether an alleged offence is proven beyond reasonable doubt is a subjective decision, about which reasonable minds may differ.
Both the defence and the prosecution can be unhappy about a decision made and there is recourse to appeal that decision to a higher court.
This means the hearing or trial will be reviewed and the judge will assess whether there was or was not reasonable doubt.
The most recent high-profile case on reasonable doubt was the decision of the full bench of the High Court of Australia in the case of Pell v The Queen  HCA 12.
The key issue in the case was that, to quote the judgment summary, although:
"the jury had assessed the complainant's evidence as thoroughly credible and reliable, the evidence of the opportunity witnesses nonetheless required the jury, acting rationally, to have entertained a reasonable doubt as to the applicant's guilt in relation to the offences."
But it is indicative of how difficult this question can be to answer that it first went through the Chief Judge and a jury in the County Court of Victoria, and then before three justices on appeal to the Court of Appeal of the Supreme Court of Victoria.
The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.