Wheels within wheels

Time Magazine:

Woodward expressed some surprise that Fitzgerald hadn't contacted him earlier in the probe, but had high praise for the prosecutor whose investigation he has openly criticized on television. During his time with the prosecutor, Woodward said, he found Fitzgerald "incredibly sensitive to what we do. He didn't infringe on my other reporting, which frankly surprised me. He said 'This is what I need, I don't need any more.'"

How can you prosecute someone for being the first to expose the identity of a person, without any proof that the press didn't already have that information? By conceding to reporters than they wouldn't have to answer any questions about who else may have revealed information to them, he's granted them an unofficial shield and given them a weapon with which to destroy others.