CBS News acknowledged memos it received about President Bush's service in the Air National Guard (search) were difficult to definitively authenticate, but said they came from "solid sources."
Some forensic experts were quoted by news organizations, including The Associated Press, saying the memos appeared to have been computer-generated with characteristics that weren't available three decades ago.
• Bush Memos (pdf)
On Friday's "CBS Evening News," anchor Dan Rather (search) said that "no definitive evidence" has emerged to prove the documents are forgeries.
"If any definitive evidence comes up, we will report it," Rather said.
The show broadcast excerpts of interviews with Marcel Matley, a San Francisco document expert, who said he believed the memos were genuine.
CBS can state "with absolute certainty" that the disputed memos could have been produced on typewriters available in the early 1970s when the memos are purported to have been written, the network said. Rather said the typeface and style of the memos were available on typewriters since well before the 1970s.
But CBS News said in a statement: "The documents are backed up not only by independent handwriting and forensic document experts but sources familiar with their content." Matley was the only expert cited, and he focused on signatures on the memos.
Matley and Rather acknowledged the memos were difficult to definitively authenticate because CBS has only photocopies, not the originals. Matley did not return a telephone message left at his office immediately after Friday's report.
At question are memos that carry the signature of the late Lt. Col. Jerry Killian (search), who was the commander of Bush's Texas Air National Guard fighter squadron. They say Killian was under pressure to "sugar coat" Bush's record, and Bush refused a direct order to take a required medical examination and discussed how he could skip drills.
Casting further doubt on the memos, The Dallas Morning News said in a report for its Saturday editions that the officer named in a memo as exerting pressure to "sugar coat" Bush's record had left the Texas Air National Guard 1 1/2 years before the memo was dated.
The newspaper said it obtained an order showing that Walter B. Staudt, former commander of the Texas Guard, retired on March 1, 1972. The memo was dated Aug. 18, 1973. A telephone call to Staudt's home Friday night was not answered.
"60 Minutes" relied on the documents as part of a Wednesday segment — reported by Rather — on Bush's service in the Texas Air National Guard from 1968 to 1973.
Former colleagues of Killian disagreed Friday on the authenticity of the documents.
One, who appeared in the TV newsmagazine segment, said Friday he did not see anything in the memos that made him think they were forgeries. Robert Strong noted he's not a forensic expert and isn't vouching for the documents.
"I didn't see anything that was inconsistent with how we did business," Strong said in an interview. "It looked like the sort of thing that Jerry Killian would have done or said. He was a very professional guy."
Both Wednesday and Friday, Strong was the only associate of Killian quoted by CBS as supporting the memo's contents.
Retired Col. Maurice Udell, the unit's instructor pilot who helped train Bush, said Friday he thought the documents were fake.
"I completely am disgusted with this (report) I saw on '60 Minutes,'" Udell said. "That's not true. I was there. I knew Jerry Killian. I went to Vietnam with Jerry Killian in 1968."
Killian's son also questioned some of the documents, saying his father would never write a memo like the "sugar coat" one.
Several of the document examiners said one clue that the documents may be forgeries was the presence of superscripts — in this case, a raised, smaller "th" in two references to Guard units.
Rather said typewriters were available in the early 1970s which were capable of printing superscripts. CBS pointed to other Texas Air National Guard documents released by the White House that include an example of a raised "th" superscript.
That superscript, however, is in a different typeface than the one used for the CBS memos. Document examiner Sandra Ramsey Lines of Paradise Valley, Ariz., who examined the documents for the AP, said she was "virtually certain" they were generated by computer.
Lines said that meant she could testify in court that, beyond a reasonable doubt, her opinion was that the memos were written on a computer.
CBS has not revealed its source or sources for the documents or the names of experts besides Matley it said examined the memos before Wednesday's report.
Bush spokesman Scott McClellan said Friday the White House, which distributed the memos after obtaining them from CBS News, was not trying to verify their authenticity. "We don't know if the documents are fabricated or authentic," McClellan told reporters traveling with the president to West Virginia.
McClellan suggested the memos surfaced as part of "an orchestrated effort by Democrats and the Kerry campaign to tear down the president."