Why Lisbon was starring at he room with the sink in episode "The Desert Rose-s06E01"...?
Well, when Lisbon enters the main room, after the pigeons thing, the door to the room with the sink was closed, then she saw Brett and tried to help him, and when the camera showed the door again, it was open, that's because RJ got out and opened the door while she was helping Brett, RJ hide behind the door while she was assisting Brett, than she looked to the door, realized it was open, and she looked inside because she was thinking, "shit..the door was closed before, I'm not alone.." but it was too late, RJ pushed her then...
And that is also how we know someone else was there, besides Brett and Lisbon..

Also, Heller told us that there was a clue at the end of that episode, I think the only possible clues are:

a) I paused the TV when it showed The GPS position of all suspects and it showed all the suspect positions before and after the anonymous phone call (probably made by RJ), Haffner, sheriff and Reed phones were moving, only Bertram, Kirkland and Stiles phones were stopped. And Kirkland was too far way and he is dead, Stiles is dying so, the only viable suspect phone that was not moving was Bertram phone. We also know that when Lisbon arrived, RJ was there, so I guess RJ phone shouldn't be moving.

b) the 666 number on the wall -> the 666 theorie that points to Bertram

c) the pigeons on the room that scared Lisbon, if RJ was the sheriff the pigeons might have scared him and that would be the reason why he didn't kill Lisbon (not betting on this one)