You might already have done this, and if not I can imagine it would be incredibly time consuming, but have you thought about contacting all LE offices to as about any unidentified people they have found, and homeless shelters to see if anyone recognizes Roger. I now LE put up info on John Does on the internet, but some must slip through the net and there might not have been the same co-operation between the states in the '80s. I am not saying I think Roger is definitly dead, just that it is a good idea to cover all bases.
Also what local publicity is there still about the case? It may be that someone who knows something is still in the area, and a publicity blitz might cause them to talk. What about going on local radio, blitzing the area with posters again (if you put them in bars it might cause people to talk when drunk).
Also can I just as if your mother definitly saw Roger get on the bus, or did she just hear the front door slam and Roger leave and then see the bus go? The same with the friend who shared the locker, did he actually see Roger there, or just see the boos and assume he had been there. I am not accusing anyone of lying, I just thought it is easy for people to make assumptions because something happens the same way everyday.
Sorry if you have already answered these questions, and I missed them. I am really sorry that you do not know where your brother is, it must seem like a never ending nightmare.