Disclaimer: I don't own Harry Potter.
Footsteps. Soft, barefoot, slapping quietly against the polished wooden floor. A heavy black cloak, slithering and rustling as the feet carry their owner across the room. A skeletal white hand, sliding into the folds of the cloak and emerging with a wand gripped in the long, pale fingers. A cold laugh from the owner of the wand. Weak-voiced pleas for mercy uttered by the prisoner, who is lying on the floor, bound tightly in thick ropes. The wand is raised. The prisoner emits a terrified scream and writhes on the ground, attempting to break free. The wand is twitched, almost carelessly, as the owner murmurs those two deadly words in a practically inaudible voice. Avada Kedavra. The prisoner becomes limp. His eyes, so recently filled with pain, stare blankly. Dead. A thin, satisfied smile on the murderer's bloodless lips. The hand stows the wand away. The feet resume their soft pattering. The next victim is sought.