Blood was splattered on the walls in an almost artistic sort of way, and three bodies lay limp throughout the living room. Doors, walls, tables, chairs, and just about everything else was being dusted for prints, and photographs being taken of the fresh carnage before the Frenchman's feet. In all the chaos of policeman running this way and that, Dupin had settled in to take a look at the crime scene for himself.
By no means did he have the authorization to be there, but he must have looked to be an investigator for he literally waltzed into the scene, blending in seamlessly with those around him. He was an investigator, to some extent, but he most likely wouldn't be asked to any official case set forth by police. He found detective work to be more of a hobby, and the affairs he looked into were more private, hence, private investigator.
One little thing distracted the man, though, and that was the fact that no one seemed to take notice of his invasive and foreign presence. It was good, since it allowed him the means to observe everything fully. But at the same time, he was disappointed that it was taking them so long to recognize him as an outsider. He wasn't very familiar with Scotland Yard, but they must have really let themselves go if a civilian such as himself could just walk into a crime scene.
c'est la vie
What more could he possibly do?