I've been mulling this one for awhile and can't help but wonder.  Did the Sens extend Bryan Murray for 3 years so he could act as a bridge to the long term plan of bringing back Peter Chiarelli?  Both contracts expire at the same time and it would probably make for a pretty smooth transition given his success with the Bruins and history within the Senators organization.

If in the next 3 seasons Chiarelli hits a bad patch and ends up canned, the Sens would easily be able to accommodate him by having Murray move up the chain within the Sens and PC takes over as GM.  If the Sens had brought in a new voice at GM they definitely wouldn't have been able to just toss that person aside and hire PC without the media having a field day with a move like that.  It would look awful if they turfed their current GM to make room for a new GM, plus it would cost whatever the buyout would be.

Update added: As per Mark's comment

While this theory may be circumstantial at best, an aspect I didn't hit on was the length of Murray's contract.  I think most Sens fans out there were gobsmacked when they found out Murray re-upped for 3 years.  The fact the term lined up with PCs contract expiring does seem interesting at least.  Murray was as good as cooked in December/January and by the end of the season gets rewarded for another 3 years.  The fact he's 68 and reupping for that kind of term does seem somewhat suspect in my estimation. 

I think of anyone in the NHL at the GM position if the Sens were to pick PC would be right up there, probably behind Holland.  PC was one of their guys and has obviously done well for himself, and if I remember correctly they weren't too keen on letting him go in the first place, but also were nice enough not to stand in his way of career advancement.