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 to do it.
Robin Westman was the 23-year-old transgender woman who is accused of opening fire through the stained-glass windows of the Annunciation Catholic Church in Minneapolis on Wednesday morning during a celebratory back-to-school mass packed with children.
Two children were killed, and 17 others injured, when the shooter sprayed bullets as the young congregants scrambled down in the pews to escape the deadly fire.
Before beginning her onslaught, Westman had reportedly used wooden planks to barricade the church's two side doors shut.
Armed with a rifle, shotgun and handgun - all used in the slaughter (and, say police, all purchased legally and recently) - Westman died at the scene of a self-inflicted gunshot wound.
