Is there any evidence saying he wasn't? They found Sam Saturday. The girls were murdered on what Wednesday or Thursday. He could have left Sam to clean up and went home. Its not an accusation its a personal belief. There were even reports of feces spread on the walls. And from what i have read its apart of a killing ritual of the occult. Sam just doesn't come off as the type of person that could orchestrate this whole mess by himself.
you say there were reports of feces spread on the walls... do you know of the source of this information, i.e. news reports? that could very well explain a part of the really foul odor Sam emitted in the company of 3 different individuals.