I think one of the reasons that RM was considered a POI (other than the close proximity and criminal history) is because he was issued a traffic ticket in Surfside the day after BD disappeared. (So, they know for a fact that he was at least in the area around the same time she was reported missing.) In addition to that, he moved into the apartment (the one LE searched) on that same day as well. IIRC, he also gave LE a hard time when they tried to ask him questions about BD ---refused to tell them where he was that day, wouldn't say if he knew anything about her disappearance one way or the other, that kind of thing.
I don't know if his previous address has ever been reported in the news. I do remember reading somewhere that he rented out an apartment at that same location, off and on for several years, but he only ever stayed for a few months at a time.