Upload & Sell: Off
It was someone you work with. (not the models or locksmith) If they would have broken into the room and taken stuff, they would have taken the entire bag. It was stolen when you first placed the bag back in the room, and I'd be willing to bet it is the person who had access that day AND who knows camera equipment. They know your workflow and probably knew that you wouldn't open the bag for several days, if not longer. They knew what to grab for max profit and or usability.
Honestly, I suspect the 24 year old.
Start contacting ALL local pawn shops and watch Craigslist. Open a new e-mail under a fake account so you can inquire about for sale stuff you might come across. Don't ask for pics of serial numbers, but ask for detailed pics of all sides of a camera/lenses. Use those to check serial numbers.
Very much along the lines of my own thinking. The 5D was in the bag 24 hours after being placed on the floor. Next time I touched the bag - Friday about 9:00am - it was gone.
Littleton Police Department secretary called to confirm serial numbers and said they have a system to check pawn shops.
The strange thing is that neither of the two guys with key access this week are really photography guys. The 24 year old is partially blind. His job is copyright related - both filing and tracking down violators. He sits at a 24" LCD but has to keep the resolution at something like 1440 x 900 to see the text. The married 29 year old does basic video editing on a MAC but never talks about still photos - and not up to date on how often the 5D MK-II and MK-III are used for HD video.
One of them may have done it for dollars but I don't think they would with the intent of using the gear.
A friend of an employee? Did they ever bring a friend in?