I have made a career out of investigating the darkest recesses of the mind. But Wednesday's atrocity, when Robin Westman shot into the Annunciation Catholic School's morning mass service, hit hard.

It's difficult to imagine a more horrific crime than killing children as they pray in church, so it will be a particular challenge trying to understand the sort of person prepared…

The shooter who attacked a Catholic school on Wednesday posted social media videos and writings that betrayed a litany of grievances and obsessions.