Debra Yang was investigating Rep. Lewis, left to work for his law firm.

I got my answer from Josh Marshall at Talking Points Memo. Prior to being hired away by Gibson, Dunn & Crutcher, the law firm defending Rep. Jerry Lewis, Debra Yang's Los Angeles US attorney office was the one supervising the corruption investigation into Rep. Lewis.

Here is from an earlier report from TPM Muckraker:

The U.S. attorney's office in Los Angeles has issued subpoenas in an investigation into the relationship between Lewis (R-Redlands) and a Washington lobbyist linked to disgraced former Rep. Randy "Duke" Cunningham (R-Rancho Santa Fe), three people familiar with the investigation said....

The government is looking into the connection between Lewis and his longtime friend Bill Lowery, the sources said. Lowery, a lobbyist, is a former congressman from San Diego.

As chairman of the Appropriations panel, Lewis has earmarked hundreds of millions of dollars in federal contracts for many of Lowery's clients, one of the sources said....

The probe focuses on what one source said was an unusually close relationship between Lewis and Lowery, who served on the House Appropriations Committee together from 1985 to 1993.

Shortly after leaving Congress, Lowery founded Copeland Lowery Jacquez Denton & White, a Washington lobbying firm whose clients include Brent R. Wilkes, a defense contractor who is the focus of a separate probe in San Diego.

Ms. Yang resigned her position as US attorney effective November 10, 2006. This was three weeks prior to the "Pearl Harbor Day Massacre" of US attorneys.

Let's put this together with the strange gap in the documents the DoJ has handed to the Congress. Again, Talking Points Memo has the story.

I think a commenter in our document dump research thread may have been the first to notice that the emails released by the Justice Department seem to have a gap between November 15th and December 4th of last year. [Snip]

The firing calls went out on December 7th. But the original plan was to start placing the calls on November 15th. So those eighteen days are pretty key ones.

More and more I strongly suspect that the entire US attorney Purge has been primarily cover for derailing the investigations into Republican corruption in Southern California.

We need to see the missing documents, and we need to get the staff at the DoJ and the White House to testify - under oath - at the Senate Hearings.

This is beginning to take on the trappings that surrounded the Watergate Hearings and the Nixon efforts to derail them.