As the U.S. government was making its case for war with Iraq back in December 2002, former U.N. weapons inspector Dr. David Kay came down squarely on the side of the Bush administration.

"Essentially, everyone who runs an active intelligence service knows this regime has been seeking weapons of mass destruction," Kay said at the time.

What a difference a year makes.

After spending seven months scouring Iraq for some trace of chemical, biological, or nuclear weapons, Kay -- who now leads the Iraq Survey Group (ISG) searching for Saddam's weapons -- has yet to find the critical evidence to back up his earlier conviction.

"We have found no actual weapons of mass destruction that exist at this point," he concedes. "But having said that ... you know how large this country is."

In "Chasing Saddam's Weapons," BBC reporter Jane Corbin -- who was given exclusive access inside the secretive Iraq Survey Group -- takes viewers inside the frustrating hunt for Saddam Hussein's alleged weapons of mass destruction. This FRONTLINE report reveals new details about what the ISG's search has -- and has not -- uncovered and questions whether the investigation's final results will justify the Bush administration's call for war.

Viewers follow Corbin and ISG officials as they conduct surprise raids and inspections throughout Iraq. She also gains access to the heavily fortified "Camp Slayer," where ISG intelligence analysts sift through mountains of Iraqi paperwork, hoping to find a trail that will lead them to some evidence of weapons of mass destruction.

David Kay admits the stakes are high. "The entire credibility of both the U.S. and ... British foreign policy and intelligence has been called into question by our inability to find the weapons immediately," he tells FRONTLINE, referring to the failure of American soldiers to find weapons of mass destruction in the weeks following the fall of Saddam Hussein's regime. "I think we all realize after Iraq we really do have to readjust our intelligence services for the new demands posed by countries like Iraq."

However, some former U.S. officials claim that it was not faulty intelligence, but the faulty interpretation of that intelligence that set America on the path to war with Iraq.

"There was obviously a faction in the U.S. government and in the U.S. intelligence community that never met a report that it considered unreliable," says former State Department intelligence analyst Greg Thielmann. "It already knew what the answer [it wanted] was."

Since the search for weapons began last spring, there have been several intelligence embarrassments -- most notably, Kay's assertion in May 2003, before joining the ISG, that two Iraqi trailers were in fact mobile production facilities for biological weapons. Despite exhaustive testing of the trailers -- which the Iraqis claimed produced hydrogen to fill weather balloons on artillery ranges -- no trace of any biological agents was found.

So, what has the Iraq Survey Group uncovered? According to its October 2003 interim report, the group has evidence that Iraq was working on long-range missiles -- a violation of U.N. resolutions. Corbin speaks with an unidentified Iraqi engineer who not only confirms that he worked on the project to build a missile with a range of 500 kilometers -- far enough to reach Israel -- but also that all evidence of the project was removed and hidden during visits by U.N. weapons inspectors.

But some Iraqi military leaders and scientists continue to strongly deny that Iraq was working on weapons of mass destruction. Corbin speaks with the wife of Iraqi scientist and presidential adviser Amer Al Sa'adi, who says that her husband repeatedly denied the existence of any such weapons. General Sa'adi is currently in U.S. custody.

"He was so convinced about what he had always said, and up to half an hour before he left and went to the Americans, he said that, 'I know there is nothing to be found, and I've always said that, and I'm repeating it again and time will bear me out,'" Helma Al Sa'adi says. "Those were his last words."

So, why didn't Saddam cooperate more fully with weapons inspectors if his country had no weapons of mass destruction? It's become one of the most frequently asked questions. Former chief U.N. weapons inspector Hans Blix suspects it was merely a miscalculated bluff.

"It's like putting up the sign on the door, 'Beware of the Dog,'" Blix says. "And you don't have a dog."