He was obviously mentally unwell. What he was unwell with doesnt really matter but there was something wrong with him. The obvious lack of empathy, the lack of insight, the lack of awareness over the seriousness of the situation, the lack of guilt, sadness, remorse, the fixation and almost relationship he formed with a character that doesnt exist, the entire fabricated reality he lived in etc all direct you towards a mental illness.
Combine that with the obvious ND. The hyperfixation and obsession with a character, the lack of empathy can feed into this, unhealthy obsessions, and irregular social skills that lead him to form connections with characters instead of people can be associated with ND.
Does any of that excuse, justify, or mitigate his actions? Of course not.
But i think it explains them. If we take away the ND is it likely he would have committed the same act? Id say probably. But if we took away the mental illness would he have done it? I dont think he would.
I think the ND is a contributing factor, and the MH is a reason, without distorted thoughts about what is and isnt real it probably would never have occurred.
Its sad all round, its sad he was never picked up on before, sad no one recognised what was happening, sad for his family he murdered, sad for his family that have to live every day with this tragedy, sad for the community knowing what he was planning to do.
i dont think what he did is excusable, and he deserves the prison sentence, but i think the MH has to be considered, as had that been recognised, and him treated and monitored, been on someones radar, it just wouldnt have happened.