Wouldn't the CIA have to have the original for authentication? Could they authenticate from a copy?
Yes, the CIA could and would do that.
Bret Baier said yesterday that ABC go the tape over the weekend and held onto it for a few days before turning it over to the feds.
If that were the case, the 'bad guys' would have to give the original to all parties -- which isn't likely to happen. In past instances, CIA has authenticated based on what has been aired on al-ja-queer tv -- I doubt the CIA obtained the "original" from ajq in those instances.