As I understand, BB&T bought most of the assets and liabilities leaving the troubled stuff for FDIC and bankruptcy court to sort out the mess. They would not buy the corporation as that would step into the place of Colonial, which I doubt anyone would be willing to do.
That is also my understanding. BBT bought selected assets (loans) and liabilities (deposits)as well as a nice Branch network, but not the stock of Colonial. As a result, BBT did not assume financial, leagal, etc. responsibility of the corporation (Colonial). The Fed. took many of Colonial's "bad" assets.