That was a surprise. I'm inclined to think that 
Brinn was just someone probably not protected by the ranger and a rather baffling no-track kill. Or then she could have been killed because of suspected rangerism. But whatever the reason, I somehow have the feeling it's not going to be revealed and even if it was it wouldn't tell who's the baddie... 

 I think I'll reread yesterDay, that's not much, after all... 
