Dafna Linzer for WaPo reports:

Some of Bush's top advisers pushed for the trade, arguing that taking custody of bin Laden's son and the others would produce new leads on al-Qaeda.
(...)
Officials have said Bush ultimately rejected the exchange on the advice of Vice President Cheney and then-Defense Secretary Donald H. Rumsfeld, who argued that any engagement would legitimize Iran and other state sponsors of terrorism.

via Josh Marshall