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Faced with numerous reports that controversial documents about President Bush’s Texas Air National Guard service were forgeries, CBS News officials stopped asserting Wednesday that the papers the network had obtained were real, and said they would “redouble” their efforts to resolve the contradictions.

CBS News President Andrew Heyward would not comment when asked if he still believed the documents, purportedly from the early 1970s, were genuine.

“I have great confidence in our sources and reporting, but obviously there are unanswered questions,” he said.

Heyward insisted Wednesday night that the network’s new efforts were not an investigation but simply “an extension of the reporting we said we’d do.”

“There are significant questions swirling around the documents,” he added. “We said all along we would continue to report all aspects of the story and this is an aspect well worth looking into.”

Even as CBS acknowledged the questionable provenance of the memos, the network asserted that the thrust of its original story aired on “60 Minutes” Sept. 8 was true: that Bush had not fulfilled his National Guard commitment 30 years ago and that he had received favorable consideration that allowed him to avoid combat in the Vietnam War.

On Wednesday night, the network aired an interview with Marion Carr Knox, who worked for 23 years at Ellington Air Force Base in Houston and served as a secretary and typist for the late Lt. Col. Jerry Killian, Bush’s squadron commander, and several other officers.

Knox, 86, told anchor Dan Rather that she had not typed the memos on which the network had based its first report. She did say that she had typed documents like them, and that Killian had been angry about Bush’s refusal to follow an order to take a physical.

Knox said later in an interview on CBS “60 Minutes” that Bush, then a young lieutenant, seemed to have a casual attitude about attending drills and that other officers in the unit were resentful of his absence.

“It seems to me that Bush felt that he was above reproach,” she told Rather. “I think it’s plain and simple. Bush didn’t think that he had to go by the rules that others did.”

The controversy surrounding CBS stemmed from six memos that the network said it had obtained from a source that it calls “unimpeachable.” Four of those memos were used in the “60 Minutes” broadcast last week.

Knox repeated earlier statements made to other news organizations that she thought the memos were fake but accurately reflected Killian’s concerns about Bush’s failure to take his physical examination in 1972 and efforts by his superiors to minimize any fallout.

The network has declined to reveal the source who provided the documents, which have been branded as forgeries by some critics and outside experts. CBS acknowledges the papers are copies, and not originals.

In New York, Heyward declined to comment on which questions the network planned to pursue about its “60 Minutes” report, but acknowledged that Knox’s statements are not particularly helpful to the network in the debate over authenticity.

“It isn’t necessarily favorable and we’re dealing with that,” Heyward said.

CBS issued a lengthy statement Wednesday evening declaring that “for now, the disagreements among `dueling experts’ have not been resolved.” The network said it had four experts authenticate photocopies of the documents before the broadcast.