When a person pleads not guilty to a criminal offence, they must advance a defence. This may be a legal defence, such as self-defence or mental illness or a factual defence such as the existence of an alibi or arguing that the accused was mistakenly identified.
In order for a person to be found guilty of a criminal offence, the prosecution must prove them guilty beyond a reasonable doubt. However, when the defence raises certain defences, the burden of proof is shifted. For instance, when the defence advances the defence of insanity, it bears the burden of proving that the defence applies. If a court is not satisfied beyond a reasonable doubt that a defence does not apply, it must find the accused not guilty.
This section of the site contains information on criminal defences.