I am not an expert on decomposition, but I would think the 9 days that they had been dead could make possible trauma less observable. According to the police, they BOTH appear to have fallen, which is extremely odd given there doesn't seem to be gas poisoning. Two falls. No observable trauma. Generally, falling suddenly would leave some trauma to the body.But killed how, with no observable trauma on either body? I just can't get into the murder scenario. Not to mention they were in a gated neighborhood which would really limit the options of who they might have encountered.
Not sure about the gated community factor. They may have known the person. Hell, it could have been a maintenance guy. An intruder is the only thing that makes sense to me right now, but it's still early in the investigation.