Damn. Killing a child is rough. That's not something you can recover from, socially, so he's going to have to ditch this place too.
Having a hair trigger and attacking before properly assessing the situation is a huge mistake in the middle of a city.
I wonder why the child was holding a knife like that while walking though, and why he sensed poison from her direction. Was she actively collecting poisonous plants that were just growing inside the city? Also, would normal people just ignore the commotion of an armed attack and pass by a guard while focused on something else?
Well, until there's actual evidence, I'm going to assume she's innocent and working hard for her livelihood. It's a bad day when you're minding your own business and the next moment you're dead.