Everyone is presumed to be innocent until they either plead guilty or are proven to be guilty. A person charged with a crime does not have to put forward a defence to be found not guilty. It is up to the Crown Prosecutor to prove beyond a reasonable doubt that the accused committed the crime. An accused can, however, choose to put forward a defence.
The accused person must have acted consciously. Crimes committed in an unconscious state are rare, but if the actions were not voluntary the accused person will be acquitted. This is called the defence of "automatism" because the person moves about automatically, without consciously controlling their actions. One such example is sleepwalking.
Someone who is very intoxicated could argue that their actions were not voluntary because they were not conscious of acting. However, there are strict limits on when intoxication can be used to show that an act was not voluntary or intentional. The Criminal Code states that even the most extreme amount of intoxication cannot be used to show that a person’s actions were not voluntary or intentional if the offence involved violence to a person.
Many crimes require an intentional act - when the accused person intended to do what they did. These crimes cannot be committed by doing something by accident as there is no criminal intent. Accidentally throwing a baseball through a window during a game of catch is not a crime, but intentionally throwing that same baseball through a window would be a crime.
A person who makes an honest mistake about the facts of a situation may not have the required criminal intent. Someone who leaves a bicycle in a bike stand, returns and rides off on another bicycle the same colour and model could use this defence. The rider was mistaken about which bike belonged them, not about whether it was illegal to take someone else's bike.
A person who has a mental disorder may not be capable of forming criminal intent if they did not understand the nature and quality of what they did or that it was wrong. In these cases they may be given an absolute discharge, a conditional discharge or be placed in a psychiatric hospital.
Some crimes require more than just the intent to perform the act in question. For example, the crime of murder can only be committed if the person intended to kill their victim. Intoxication could reduce a crime of murder to manslaughter, if the person could not form the intent to kill someone because they were intoxicated.
An innocent bystander, forced at gunpoint to drive the getaway car after a bank robbery, might use the defence of duress.
A person who commits an offence because they were threatened may claim the defence of duress. Generally speaking, courts will consider how immediate and serious the threat was, whether there was a reasonable legal alternative, and the degree of harm avoided by way of comparison to the offence itself. Duress may not be a defence to violent crimes such as sexual assault, aggravated assault or murder.
Provocation is something that causes another person to lose their self-control. It can be an act or an insult. Provocation can reduce a charge of murder to manslaughter. This is the only time a person may use provocation as a defence. An accused person who acts on provocation before "cooling off" may be acquitted of murder and convicted of manslaughter. If too much time passes between the provocation and the offence, the defence of provocation may not be available. Even so, evidence of provocation can lessen the sentence if the person is convicted.
An alibi is when an accused person claims that they were not present at the time of the offence. Independent evidence supporting this claim strengthens an alibi defence.
A person who is attacked may use force to resist the attack. The person may use only the amount of force necessary to defend against the attack. This is called "reasonable force". A person charged with assault, murder or manslaughter may use this defence.
Defence of property is similar to self-defence. A person may use reasonable force to prevent someone from entering their home or property. A person defending their property may not use excessive force. This defence cannot justify shooting, stabbing or setting traps that would injure a trespasser.
Ignorance of the law is no excuse. Not knowing that something is a criminal offence does not mean it is all right to commit the offence. But when an accused person can show that a government official misled him or her about the law, an exception called "officially induced error" may apply and mistake of law may provide a defence.
A person who does an illegal act to prevent a more serious result may raise the defence of necessity. There are several conditions. The accused must show that the act was done to avoid a greater evil; that there was no alternative; and that the illegal act was not more than necessary to avoid the evil.
A person who has been tried for an offence cannot be tried again for a similar offence arising out of the same facts. That person may plead a special plea that they have already been acquitted, convicted or discharged. The Canadian Charter of Rights and Freedoms also gives this right.
The police may carry out undercover activities to detect crime. In doing so, legally they may present a person with the opportunity to commit a crime, but they may not harass, bribe or otherwise induce the person to break the law. Police conduct that induces criminal behaviour is called entrapment. The accused person must prove entrapment.
Entrapment is an abuse of process. It is so unfair and shocking to our sense of justice that it would be an abuse to force the accused person to stand trial in these circumstances. After accepting that there was an abuse of process, the judge "stays" or stops the trial.