I guess this is one of the cases that will fascinate/feed conspiracy theorists for many years, because it has all the ingredients they dream about.
Ultimately, I think his actual death was either self-inflicted, or part of a consensual act that went wrong. I don't buy the idea that his colleagues did nothing about his absence for a week, but really see it as being fairly reasonable in the circumstances that someone would have been tasked to covertly a) check up on him, and b) make sure there was nothing in his flat that shouldn't have been there. If a another party was inadvertently involved in the death, especially if it was someone in the same sensitive line of work, it would make sense if they cleaned up after themselves, or had someone else do it for them.
If it was actually murder, then it's either totally unconnected to his work, or else it wasn't an "inside job," for the simple reason that it's just too damn weird and obvious a way to kill someone.
The denialism about the bondage/fetish angle just seems to be to placate the feelings of the family/friends, who have been highly outspoken about Williams being "straight" and "normal."