One thing that come to my mind, in the composition... Isn't the rope a bit too long to actually feel like he's not noticed? As the perspective is twisted (like a camera objective), the down end of the rope show the actual location of the assassin, from the floor view. And I find that end of the rope quite close to the guards field of vision. Especially with the lights that are around. Those are candles... which mean lot of sources of fire to catch any curious eyes at every flicks of those tiny source of lights. From the view in the next room, it's a day time scene in a closed room, so people are even more sensible to notice light switch and moving shadows.
There is a lot of complex interrogation that comes from my mind while I look a this picture. But outside those "scenaristic" questions, it's a really good piece of work!