The other aspect of the "suicide" theory that doesn't seem to fit is the fact that if RM did in fact do that, wouldn't you think he would have been "found?" Same with his being killed by a robber or the likes, then where is he?? This is all so morbid, but if that were the case, someone would had to have taken great care to hide the evidence, which of course could have happened. It wouldn't likely have been a random crime, I would guess.
I guess I am leaning toward RM's leaving voluntarily, holes in the story and all!