A study was conducted to investigate and identify differences inherent in two subtypes of psychosis driven or mentally disordered homicide: matricide versus any other biological intrafamilial homicide or attempted homicide. Matricide was further investigated through the exploration of offence specific details, as well as demographic and diagnostic characteristics of persons who had committed (or attempted) homicide against the mother and were subsequently found not criminally responsible and detained by the Ontario Review Board between 1992 and 2012. Matricidal accused were more often diagnosed with childhood disorders and paranoid schizophrenia. As adults, they failed to mature sexually and socially, and continued to live at home, dependent on the mothers that were the ultimate victims of their violence. Attachment theory is offered as a proposed explanation for the matricidal impulse.