In a NIE just two years ago, the U.S. Intelligence Community ("IC") concluded: "[We] assess with high confidence that Iran currently is determined to develop nuclear weapons despite its international obligations and international pressure, but we do not assess that Iran is immovable." However, the latest NIE on Iran's nuclear program says, "…we do not know whether (Iran) currently intends to develop nuclear weapons." This is just one of many differences between the 2005 estimate, which concluded that Iran was pursuing a nuclear weapons program, and this latest estimate, which claims that the "military" nuclear weapons program was shut down sometime in 2003. (Keep in mind that the "civilian" program, which everyone concedes is still up and running, could quite easily be repurposed for military use. And the NIE is drawing a line between the two without explaining how it made that judgment. See Question #3 here.)

What changed?

Judging from press accounts, anonymous intelligence officials are offering a number of answers.
For example, McClatchy newspapers ran this description (emphasis added):

Senior U.S. intelligence officials said the judgment that Iran had halted its nuclear weapons program in mid-2003 emerged four to six months ago as a result of fresh intelligence, some of it from open sources and some from a "very rigorous scrub" of 20 years of information, some of which informed the 2005 NIE.

The officials, who spoke on condition of anonymity because of the sensitivity of the issue, said the analysts who drafted the report also had applied lessons learned from an erroneous 2002 NIE on Iraq.

Taken at face value, we have here a number of explanations. What is the "fresh intelligence" gathered by the IC? I am a strong advocate of open source analysis, but what "fresh intelligence" was gathered through open sources (e.g. press articles, television appearances, etc.)? Can you determine through open sources that Iran shut down its nuclear program in 2003? If so, how?

What did the "very rigorous scrub" of two decades of information entail? Keep in mind that the U.S. and the international community were in the dark for much of this period concerning Iran's nuclear program. And why did this scrub produce different results now since it also "informed the 2005 NIE"? Is this a concession that the tradecraft used in the 2005 estimate was sloppy? Or, have the analysts let the current climate, with partisan debates over how to handle Iran dominating the headlines, dictate the way they viewed this intelligence?

This last question is particular apt, since the McClatchy account tells us that the "analysts who drafted the report also had applied lessons learned from an erroneous 2002 NIE on Iraq?" Did the lessons have to do with tradecraft? Or, do they mean they just wanted to make sure that the intelligence coming out of the IC was not used to justify any military action, as it did in the case of Iraq?

The Washington Post, based on anonymous sources, gives us a sense of what intelligence was used in the revised estimate (emphasis added):

Senior officials said the latest conclusions grew out of a stream of information, beginning with a set of Iranian drawings obtained in 2004 and ending with the intercepted calls between Iranian military commanders, that steadily chipped away at the earlier assessment.

In one intercept, a senior Iranian military official was specifically overheard complaining that the nuclear program had been shuttered years earlier, according to a source familiar with the intelligence. The intercept was one of more than 1,000 pieces of information cited in footnotes to the 150-page classified version of the document, an official said.