WASHINGTON (CNN) -- Iranian military officers' notes and conversations intercepted by the United States played a significant role in the new U.S. assessment of Iran's nuclear weapons plans, officials told CNN.
Officials say public information about Iran's Natanz facility was part of a new intelligence report.
One senior official said there was no "Wow, we have it!" moment -- that it was a "continuous stream" of information that led analysts to go back and "scrub" old information. Another senior official said there was no "single strand of anything" that produced the change in the assessment.
In the National Intelligence Estimate released on Monday, the U.S. intelligence community dramatically reversed course, going from "high confidence" two years ago that the Islamic Republic was working toward nuclear weapons to a new assessment -- also with "high confidence" -- that Iran stopped its weapons program in 2003.
The new information came from a variety of areas, including human sources, intercepted communications, and materials available to the public, according to government officials familiar with the NIE.
In particular, the United States came into possession of notes from Iranian military officers, an intelligence official and a senior military official told CNN.
In addition, two intelligence officials told CNN the National Security Agency intercepted discussions among senior Iranian military officers about the lack of a nuclear program.
Publicly available material that factored into the new assessment included a 2005 press tour of Iran's Natanz centrifuge facility. "We actually ended up with photography of all of the equipment there. ... We actually had data," an official said.
Some of the new information challenged previous conclusions and helped illuminate old data. For example, newly acquired data helped analysts understand the significance of data obtained in 2004 from an Iranian computer that included documents and diagrams related to nuclear warhead designs.
One government official said there was also more rigorous analysis. The analysts worked "hand in hand" with spies and had a much better idea about the sources of the information than they did about the sources of the now-discredited 2002 National Intelligence Estimate on Iraq's weapons of mass destruction.
That hastily prepared NIE -- used to justify the March 2003 invasion -- concluded Iraq had active weapons of mass destruction programs, but no evidence of such programs has ever been discovered. One senior intelligence official said the current analytical process was "much more robust" as a result of the 2002 experience.
The NIE released this week was almost ready for release in the spring of 2007, drawing conclusions very similar to the 2005 version of the NIE, officials said. CNN was told in July that new information had delayed the anticipated release, and Director of National Security Mike McConnell indicated last month that new information started coming in as work on the estimate was coming to a close.
Officials told CNN that, armed with the new data, analysts went back and "scrubbed" their assumptions and inferences. Groups known as "red teams" were formed to present alternative viewpoints and challenge earlier assessments. Counterintelligence officers reviewed the data for evidence of any disinformation or strategic deception on Iran's part to conceal its program.
In the end, after discussions described as "spirited," the analysts concluded with high confidence that the Iranians had ended their nuclear weapons program.
But senior intelligence officials had to be convinced. One of those officials indicated CIA Director Michael Hayden and his deputy, Steve Kappas, brought together the analysts who were drafting the NIE about four to six weeks ago.
"It was kind of a show-me," the official said. "We were a skeptical audience."
Another senior intelligence official called Iran "probably the hardest intelligence target there is," suggesting it is even more difficult than North Korea. The official said Iran "deliberately, carefully and for some period of time effectively kept hidden" its nuclear weapons program.
Questions have also been raised about whether President Bush was aware of the change in assessment before his comment in October suggesting Iran still had an active weapons program.
At a news conference Tuesday, Bush said McConnell told him in August that there was new information on Iran, but didn't tell him what it was. The president said he was briefed last week on the key judgments of the completed NIE.
But White House spokeswoman Dana Perino said Wednesday that McConnell told Bush during the summer that Iran "may have suspended" its nuclear weapons program, but that analysts needed more time to study new data before they came to a conclusion.
The chairman of the Senate Intelligence Committee, Sen. Jay Rockefeller, D-West Virginia, said Tuesday that both he and the committee's vice chairman, Sen. Kit Bond, R-Missouri, were given information on Iran several months ago but were not told of any final conclusions.
"I have to believe that [Bush] knew what was going on before Vice Chairman Bond and I did," Rockefeller told PBS's "The NewsHour with Jim Lehrer."
Senior intelligence officials admit there are still gaps in what they know about Iran's nuclear weapons program. But they insist better analysis and new information that was not known at the time of the 2005 assessment are what led to the about-face in the new NIE. E-mail to a friend
CNN's Barbara Starr and Ed Henry contributed to this report.