CBS News admitted Monday that it can't confirm the authenticity of documents it cited in a report questioning President Bush's military record. The New York-based news operation, a unit of Viacom ( VIA), now says its source for the documents "admits that he deliberately misled the CBS News producer working on the report." The turnabout comes nearly two weeks after "60 Minutes" broadcast a Sept. 8 piece on the president's National Guard service. After initially brushing off questions about the segment, CBS last week started an investigation into the matter and said it would seek to get to the bottom of the dispute. "Based on what we now know, CBS News cannot prove that the documents are authentic, which is the only acceptable journalistic standard to justify using them in the report," CBS News President Andrew Heyward said in a statement Monday. "We should not have used them. That was a mistake, which we deeply regret." Dan Rather, the CBS News anchor who reported the story for "60 Minutes," issued an apology. "We made a mistake in judgment, and for that I am sorry," he said. "It was an error that was made, however, in good faith and in the spirit of trying to carry on a CBS News tradition of investigative reporting without fear or favoritism." CBS also said it was commissioning an independent panel to review the incident and would announce the name of the participants shortly.