I've played through the Coldridge Prison/Sewers mission FIVE TIMES NOW. I take so much care and time doing everything right, and at the end, it says I have 1 hostile kill. I HAVEN'T KILLED ANYBODY. I knock them all unconscious and hide them, I place them carefully down so they don't die, I don't even have my blade out most of the time. Can anybody help?

I also pretty much step-for-step copied a guy on Youtube who succeeded doing the first mission without killing anybody and I still have 1 kill!