Veriadne

I'm sure I'm missing something. I've been playing all three factions, and I went ahead and met and helped some of the infiltrators, but now I'd like to turn coat and kill them... only I can't seem to find a way to make the game allow me to. With Shaftoe and Eliza, I had to attack Eliza before I was able to attack Shaftoe (which was automatic at that point as soon as I got near him). Is there one Infiltrator I have to take out first in the same way?