For the benefit of the lurkers, here is an admission of the Federal Commissioner of Exchange, General Benjamin "Beast" Butler concerning prisoner exchange:
In case the Confederate authorities should yield to the argument...and formally notify me that their slaves captured in our uniform would be exchanged as other soldiers were, and that they were ready to return to us all our prisoners at Andersonville and elsewhere in exchange for theirs, I had determined, with the consent of the lieutenant-general [Grant], as a last resort, in order to prevent exchange, to demand that the outlawry against me should be formally reversed and apologized for before I would further negotiate the exchange of prisoners.It may be remarked here that the rebels were willing enough to exchange prisoners at this time, man for man, were we to permit it to be done.