(CNN) -- Former Secretary of State Colin Powell said Wednesday that U.S. intelligence officials should be questioned over their handling of "Curveball," an Iraqi defector whose now discredited claims on weapons of mass destruction helped fuel the Bush administration's drive to war in 2003.

It has become clear over the years that "the source called Curveball was totally unreliable," Powell said in a statement to CNN.

"The question should be put to the CIA and the DIA (Defense Intelligence Agency) as to why this wasn't known before the false information was put into (a key intelligence estimate) sent to Congress, the president's State of the Union address and my February 5 presentation to the U.N."

Powell, in an address to members of the United Nations Security Council in February 2003, said the U.S. government had "first-hand descriptions of biological weapons factories on wheels."

"The source was an eyewitness, an Iraqi chemical engineer who supervised one of these facilities," Powell said at the time. "He actually was present during biological agent production runs. He was also at the site when an accident occurred in 1998. Twelve technicians died."

Two months later, the invasion of Iraq began. No biological weapons, no germ labs, and no weapons of mass destruction were found.

The defector, Rafid Ahmed Alwan al-Janabi, has admitted in an interview with Britain's Guardian newspaper that he lied to help bring down Saddam Hussein's regime.

"I had the chance to fabricate something, to topple the regime," he said. "I did this, and I am satisfied, because there is no dictator in Iraq anymore."

When Alwan spoke to CNN in 2008, he said, "I never told anyone Saddam Hussein was producing weapons of mass destruction."

At the time, intelligence sources told CNN that Alwan had claimed that Iraq had a secret bioweapons program. But now, Alwan admits that after he was granted asylum in Germany in 2000, he used his training as a chemical engineer to concoct for his debriefers a story of Iraqi WMD production.

Although the CIA was not given a chance to interview Alwan directly, and German officials had questioned some aspects of Alwan's story, his assertions were included in the material provided to Powell for his U.N. presentation.

Tyler Drumheller, who was the CIA's chief of European operations at the time, agrees that the "Curveball" information was not well-enough vetted. He says he had reservations at the time about relying on it, but that when he asked for direct CIA access to Alwan through the German intelligence service, he was rebuffed.

A representative of Germany's intelligence service declined to comment.

Drumheller claims top Bush administration officials were too willing to believe Alwan's story "because that was the only piece of intelligence they had that really fit what the administration was looking at."

Former President George W. Bush declined through a spokesman to comment. Representatives for former Vice President Dick Cheney, former Defense Secretary Donald Rumsfeld, and the DIA did not reply to CNN's inquiries.

Former CIA director George Tenet, who was Drumheller's boss, wrote in his memoirs that "perhaps some people's recollections of 'if only someone had listened to me' have become sharper than reality." Without naming names, Tenet said that "concerns about Curveball did not get disseminated far and wide through the agency as they should have been."

Former Homeland Security adviser Frances Townsend says that the U.S. government should seek Alwan's extradition and prosecution, for "intentionally lying and deceiving the U.S. government."

"It absolutely makes my blood boil," she told CNN.

Not all observers are accepting Alwan's claim that his goal in spinning his WMD tale was to free the people of Iraq from Hussein.

"He told the story because he wanted to get out of a refugee camp in Germany," said Bob Drogin, author of a book about the episode. "He wanted to get his wife out and bring her to Germany, he wanted to get citizenship, and he wanted a Mercedes Benz. And he got all of those things."

But in his interview with the Guardian, Alwan said he had already won asylum before he spoke to German intelligence about weapons programs in Iraq, and that telling them his story did not win him a life of ease.

Alwan insisted he is proud of the role he played in the toppling of Hussein. In the video of the interview posted online, he said that if he had it all to do over again, he would say the same thing "because I wouldn't want that regime to continue in our country."

CNN's Frederik Pleitgen and Pam Benson contributed to this report