Finding Iraq's "smoking gun" - the large quantities of chemical, biological, and other weapons the US cited to help justify a war - was supposed to be a certainty.
Instead, the search is turning out to be a puzzle. The surprising difficulty and complexity of the weapons-sleuthing has already caused a rethinking of the initial inspections effort that began even before the war started.
Just weeks into the search process, the effort is being overhauled to reach beyond the early focus on suspected weapons sites - which have largely turned up "dry" - to a greater emphasis on intelligence and detective work. A Defense Department official says a team of perhaps 2,000 specialists will interrogate former Iraqi officials, interview key Iraqi scientists, and comb through documents - which might shed light not only weapons but on links between Saddam Hussein's regime and terrorist organizations.
"What we're seeing is the transition from the Easter egg hunt to the complex, more analytical and expert-driven phase of the operation," says Gary Samore, an expert on nonproliferation at the International Institute for Strategic Studies in London. "The first wave of military personnel was good at searches. The problem is, nothing substantial has come up."
The lack of any big hits is worrisome for more than just the morale of the search teams. The lack of hard evidence of the ousted Iraqi regime's weapons is also raising questions about the credibility of prewar assessments by President Bush and Secretary of State Colin Powell.
Beyond that, it is also casting doubts over the quality of US intelligence and about the quality of planning for the weapons search.
With pressure to produce results mounting, the Pentagon plans to modify and expand the operations beginning next week.
The Pentagon plans to augment the 75th Exploitation Group - made up of some 600 people from the military, CIA, Defense Intelligence Agency, and FBI - more than tripling its size. This Iraq Survey Group will be led by the DIA's Maj. Gen. Keith Dayton.
The group will have a "fusion cell" housed within the DIA made up of US government experts. "Their job is going to be to do that kind of in-depth analysis that's necessary in order to make this a successful effort over time," Stephen Cambone, Defense undersecretary for intelligence, told reporters last week.
So far, the 75th Exploitation Group has visited about 70 of 600 sites on its original top-priority list - without finding the "smoking gun" of unconventional arms. The most interesting piece of equipment discovered so far is an Iraqi trailer that was turned over to the US by Kurds in northern Iraq on April 19.
"The Kurds reported to us that the trailer may have been in the company of military vehicles ... along with a decontamination truck," said Mr. Cambone. He added that there were "common elements" between a defector's statement that was used in Secretary of State Colin Powell's February presentation to the UN Security Council and the mobile production facility.
"While some of the equipment on the trailer could have been used for purposes other than biological weapons agent production," Cambone said, "US and UK technical experts have concluded that the unit does not appear to perform any function beyond ... production of biological agents."
The trailer was brought from Mosul to Baghdad, where it is undergoing more extensive testing. It is likely to take weeks before results are available.
The time it is taking to substantiate the dire early claims of Iraq's weapons holdings is not a surprise to all weapons experts. But it is causing a certain discomfort in the Bush administration.
The complexity of weapons inspections always meant surprises were in store, even in a presumably amply scrutinized country like Iraq. "I've been saying for several months that I expected to find chemicals and filled missiles, bombs, or 122mm rockets filled with chemicals," says David Franz, a former UNSCOM inspector who now works for the University of Alabama. "But I wouldn't be shocked if we didn't find biologicals."
Dr. Franz explains that it's very easy to destroy biological agents because they are normally produced in such small quantities. He says that during the first inspection period in the early 1990s, under UNSCOM, investigators looked for biological warfare programs - something the size of a factory. But in the later 1990s, under UNMOVIC, inspectors were looking for "something the size of your kitchen and a weapon smaller than a toaster."
Still, the slow progress on the weapons front is causing jitters in Washington - worrying some officials that cases against other states suspected of weapons proliferation may now be more difficult, or that the American public may doubt future claims of dangers from countries with weapons programs.
President Bush, in his January state of the Union speech, said Iraq had hundreds of tons of chemical weapons, tens of thousands of missile warheads, and tens of thousands of liters of biological weapons, anthrax, and botulinum toxin among them.
Similarly, Secretary Powell captivated television audiences around the globe with a little vial of mock anthrax he displayed at the Security Council in February
It created a vivid picture of a fearsome threat for a nation and a world where "WMD" - for weapons of mass destruction - had become household jargon.
Like Alabama's Franz, Mr. Samore in London says "no one should be surprised" that no biological agents have been found. "The big surprise so far," he says is that neither large stocks of munitions or chemical agents - both more difficult to dispose of or hide - have turned up.
That doesn't mean the evidence cited in the prewar months was fabricated. "I really don't think anyone did that," Samore says. It could mean arms remain hidden, were moved out of Iraq, or that the regime destroyed them. "We still don't know."
Other experts say the slow search is a reminder that the US suffered from inadequate intelligence and was outmaneuvered by Mr. Hussein in the past. For example, it was the 1995 defections of Iraq's secret weapons chiefs, who were Hussein's sons-in-law, that led UN inspectors to learn that Iraq was about four years ahead of where they thought it was in its WMD programs.
"Everyone from Colin Powell on was talking about ... all the materials the UN knew Saddam had at one point and for one reason or another resisted accounting for," Samore says.
He expects that puzzle to be more complete "in six months to a year. It's going to take a lot of work."