The terminology in Canada "not criminally responsible reason on account of mental disorder" (NCRMD) (Criminal Code, s. 16). A finding of NCRMD is a special verdict that results in the accused being placed under the jurisdiction of the Review Board.1
Assuming for the sake of analysis that such an outcome is made out in the circumstances that you've described (much would depend on the expert evidence), such an outcome would not necessarily lead to indefinite detention.
The options available are:
- absolute discharge;
- conditional discharge; or
- detention in custody in a hospital
And even when in detention in a hospital, there is a regular review and the person is released when detention is no longer necessary for public safety.
The burden is not on the detained to show that the chance of a repeat is essentially zero. That would be a great exaggeration of the barrier to release and incorrectly reverses the burden. Instead, the Review Board must find evidence that there is a significant continuing risk to the public, at the time of the hearing, in order to keep the person in custody. There is no burden on the accused or on anyone to rule out future occurrences with any certainty.
Latimer and Lawrence explain:
The Supreme Court of Canada further clarified in R. v. Winko that Section 672.54 does not create a presumption of dangerousness. In other words, while the protection of society is paramount, there must be clear evidence of a significant risk to the public before a court or Review Board can maintain control over an accused through the imposition of a conditional discharge or detention order.
Some extracts from Winko:
Restrictions on his or her liberty can only be justified if, at the time of the hearing, the evidence before the court or Review Board shows that the NCR accused actually constitutes such a threat
there is never any legal burden on the NCR accused to show that he or she does not pose a significant threat to the safety of the public
A past offence committed while the NCR accused suffered from a mental illness is not, by itself, evidence that the NCR accused continues to pose a significant risk to the safety of the public.
1. This is one major difference between NCRMD and the defence of automatism, which is a defence based on negation of the elements of the offence and would result in a standard acquittal if successful, with no jurisdiction for the Review Board to impose detention or conditions.