Perry was hired by LeBeau in Pittsburgh (after being a very good safety for them) and was considered on a fast track to coordinator-ville and an eventual HC. But when Tomlin replaced Cowher, he dumped some existing coaches to put in his own people. LeBeau wouldn't comment, saying it was the HC's call.
It was an interesting maneuver, because Pittsburgh gives its defensive staff a huge amount of sway in personnel and roster moves. Tomlin was not allowed to pick his own D coordinator or scheme despite (I think) a background in defense.
Perry might have been out the door already and LeBeau was able to pass it off as an HC exercising his hiring discretion. But up to the dismissal, he was very well thought of. There were no rumors at the time that he was on the outs. New HC coaches like to have people they know on both sides of the ball, hence Winston Moss on D.
It looked like a coup at the time. But he hasn't been delivering.