But Bush told investigators that he was unaware that Cheney had directed I. Lewis "Scooter" Libby, the vice president's chief of staff, to covertly leak the classified information to the media instead of releasing it to the public after undergoing the formal governmental declassification processes.

Bush also said during his interview with prosecutors that he had never directed anyone to disclose the identity of then-covert CIA officer Valerie Plame, Wilson's wife. Bush said he had no information that Cheney had disclosed Plame's identity or directed anyone else to do so.

As to why Libby would lie to the FBI and grand jury:

One obvious reason, prosecutors have believed, is that Libby did not want to admit that he was disseminating material gleaned from classified information. Even if Libby believed that he was unlikely to be charged with disclosing classified information, the investigators think that Libby could have feared the loss of his security clearance or his job. Or, perhaps most important of all, he worried about embarrassing Cheney and Bush.

Sources say investigators believe it is possible that Libby was trying to obscure Cheney's role in the Plame leak -- either by the vice president directing Libby to leak her CIA status, or through a general instruction from Cheney encouraging Libby to get the word out about Plame's role in sending Wilson to Niger. They say it is also possible that Libby lied to conceal the fact that he leaked Plame's identity to the press without Cheney's approval.

Another interesting note:

A senior government official who has spoken to the president about the matter said that although Bush encouraged Cheney to get information out to rebut Wilson's charges, Bush was unaware that Cheney had directed Libby to leak classified information....."[Libby] further testified that he at first advised the Vice President that he could not have this conversation with reporter Miller because of the classified nature of the NIE. [Libby] testified that the Vice President later advised him that the President had authorized [Libby] to disclose the relevant portions of the NIE."

And Libby "testified that he spoke to David Addington, then Counsel to the Vice President, whom [Libby] considered to be an expert in national security law, and Mr. Addington opined that presidential Authorization to publicly disclose a document amounted to a declassification of a document."

Crooks and Liars has some good analysis of Murray's new article.