Constitutional law has a pervasive and foundational influence on criminal law and it is relevant at all stages of the criminal process. The division of powers limits the enactment of criminal law to Parliament
but allows provinces and municipalities to enact regulatory offences. Sections 7 to 10 of the Charter restrain the investigative activities of the police. These rights are enforced primarily by the decisions of courts under section 24(2) of the Charter to exclude unconstitution-ally obtained evidence if its admission would bring the administration of justice into disrepute. In the Charter era, Canadian courts are also prepared to stay proceedings if the accused has been entrapped into committing a crime. At the same time, the entrapment defence allows police to offer people an opportunity to commit a crime so long as they have a reasonable suspicion that the suspect is engaged in criminal activity or the suspect is present in a high-crime area. Even if they have a reasonable suspicion or are acting on a bona fide inquiry into crime, the police cannot actually induce the commission of a crime by shocking activity that would bring the administration of justice into disrepute.
The Charter affects the trial process by giving the accused various rights including the right to make full answer and defence and the right to be presumed innocent. The presumption of innocence is violated whenever the accused has to establish an element of an offence or a defence on a balance of probabilities because this allows a conviction to occur despite a reasonable doubt. Even mandatory presumptions that can be displaced by satisfying an evidential burden violate the presumption of innocence. At the same time, the courts have frequently accepted limitations on the presumption of innocence as reasonable limits and have, on their own initiative, required the accused to establish the defences of extreme intoxication and automatism on a balance of probabilities.
The Charter also affects substantive criminal offences that infringe freedom of expression, are excessively vague, overbroad, arbitrary, grossly disproportionate, or allow the punishment of the morally innocent. These matters will be discussed in greater depth in subsequent chapters, it should be noted that section 7 of the Charter is offended by imprisonment of the morally innocent who have committed a prohibited act but through no fault of their own. The courts have found that...