Perhaps because Li was never convicted of a crime but was determined to be Not Criminally Responsible on Account of Mental Disorder (NCRMD) and placed in a treatment regime as mandated by Parliament “for an act committed or an omission made while suffering from a mental disorder that rendered the person incapable of appreciating the nature and quality of the act or omission or of knowing that it was wrong.” 

In this case both the Crown and defense counsel agreed Li met the definition of NCRMD (as did all the psychiatric experts) and made joint submission to the trial judge.

It is a fundamental principle of criminal law that one must have the requisite 'mens rea' to commit a crime... any crime and in Li's case this was absent.  This principle dates back many centuries in English law and we have passed a version of the  M'Naghten Rule into our Criminal Code when it was first drafted.  Queen v. M'Naghten, 8 Eng. Rep. 718 [1843]

We do not punish persons who are found NCRMD.