Take out the nearest guards, just to be safe.
From Create Your Own Story
You slide your hand down to the knives you keep at your waist and slowly approach the guards from behind. They're distracting themselves with small talk about their day, but you realize kill them here would leave evidence; this spot is crossed by almost all the other guards in the area. You need to take them out without blood. There's a loose brick you can use to knock them out, or you can make some noise and draw them into an alley, away from the eyes of other passing guards.
