Last month we noted a possible motive behind Scooter Libby's alleged obstruction of justice and perjury: he thought he could mislead prosecutors without retribution because reporters would never go back on their pledges of confidentiality. Now, The Washington Post's Carol D. Leonnig and Jim VandeHei note another possible motive behind Libby's alleged activities.

In the opening days of the CIA leak investigation in early October 2003, FBI agents working the case already had in their possession a wealth of valuable evidence. There were White House phone and visitor logs, which clearly documented the administration's contacts with reporters.

Libby, according to Fitzgerald's indictment, gave a false story to agents and, later, to a grand jury, even though he knew investigators had his notes, and presumably knew that several of his White House colleagues had already provided testimony and documentary evidence that would undercut his own story. And his interviews with the FBI in October and two appearances before the grand jury in March 2004 came at a time when there were increasingly clear signs that some of the reporters with whom Libby discussed Plame could soon be freed to testify -- and provide starkly different and damning accounts to the prosecutor.

To critics, the timing suggests an attempt to obscure Cheney's role, and possibly his legal culpability. The vice president is shown by the indictment to be aware of and interested in Plame and her CIA status long before her cover was blown. Even some White House aides privately wonder whether Libby was seeking to protect Cheney from political embarrassment. One of them noted with resignation, "Obviously, the indictment speaks for itself."

In addition, Cheney also advised Libby on a media strategy to counter Plame's husband, former ambassador Wilson, according to a person familiar with the case.

In related news, National Journal's Murray Waas, who has provided some of the best coverage of the Plame investigation, today writes that Libby might be the key the investigation of Karl Rove. So if Libby is still interested in a plea and is willing to turn on his fellow compatriots, it looks like he could have quite a bit of leverage with special prosecutor Fitzgerald.