During a valedictory appearance with David Letterman, Dan Rather (search) pointedly ducked a question about whether CBS News President Andrew Heyward should have quit after last fall's discredited story about President Bush's military service.

About half of Rather's "Late Show" (search) guest shot Thursday was spent talking about the story and the independent investigation into how it got on the air despite the use of documents CBS ultimately couldn't vouch for.

Rather, 73, will anchor his last "CBS Evening News" broadcast Wednesday, the 24th anniversary of when he took over from Walter Cronkite.

The story's producer was fired and three CBS News executives were asked to resign for their roles. Heyward kept his job after CBS Chairman Leslie Moonves (search) concluded he had been failed by the people who worked for him.

Rather said the people who lost their jobs are "never very far from my mind."

He paused when Letterman (search) asked him whether the CBS News president should have "taken a bullet" and stepped down.

"He's on vacation right now," Rather said, "but when he gets back you can ask him."

Before he became CBS News president, Heyward was Rather's executive producer at the "CBS Evening News."

Rather said that to his mind, two of the panel's most important conclusions were that it could not demonstrate that political bias played a part in the stories or conclusively account for the origins of the documents in question.

CBS's Sept. 8 story began falling apart when experts questioned the legitimacy of documents supposedly written by Bush's National Guard commander that suggested the future president had received preferential treatment.

"Although they had four months and millions of dollars, they could not demonstrate that the documents were not authentic, that they were forgeries," Rather said.

He declined to give his opinion of Moonves' decision to oust the four employees.

"It's behind us," Rather said. "We have to look forward at some point. You know, you've had ups and downs in your career, you've had criticisms. Sometimes you think it's justified, sometimes not. But at a certain point you have to say, the panel has spoken, the corporate leadership has spoken, this is how it is."

Letterman warmly thanked Rather for several years of guest appearances. "If it'll help," he said, "I'll step down."

Rather laughed. "You're a profit center, Dave, don't step down," he replied.