The DOJ forced everyone in the administration to sign waivers freeing the reporters of any confidentiality agreement a long time ago. Cooper said he didn't accept that piece of paper.

Time released the reporters notes which indicated Rove was a source pretty much flew in the face of repeated denials by the White House left them with no option. Cooper *then* is said to have received what he called a valid waiver from Rove. So pretty much key here was Time giving up the notes.