Former Secretary of Defense Donald Rumsfeld said Sunday that the Bush's administration's erroneous belief that there were weapons of mass destruction in Iraq was not the only reason for invasion, but it was "the big one."

"I think the concern I had that the information we had was imperfect," Rumsfeld told CNN's Candy Crowley.

"It was more than imperfect," Crowley interrupted. "Some of it was just flat wrong."

An Iraqi defector, codenamed Curveball, who allegedly helped convince the Bush administration that Saddam Hussein had a secret stash of biological and chemical weapons, admitted this week that he made it all up.

Rafid Ahmed Alwan al-Janabi told The Guardian that he invented the stories to help topple Saddam Hussein, but was shocked when the US used tales as an excuse to go to war.

"Well, the intelligence community talks to hundreds of people," Rumsfeld explained. "They have human assets such as this man. Some are honest. Some are dishonest. Some do it for money and some do it for self-aggrandizement and some just lie."

"Did anyone say 'give me the person who gave the intelligence' because sitting here listening to you, to me, the fault of the war was the intelligence community -- the false premise of the war?" Crowley asked.

"Well, first of all, there were a variety of reasons for the war, not simply WMD," Rumsfeld replied. "If you looked at the resolution from the Congress, there were multiple reasons, and if you looked at the UN resolution, there were multiple reasons so it wasn't a sole reason."

"But it was the big one," Crowley observed.

"No question it was the big one," Rumsfeld agreed.

"I think probably people would argue to you that we wouldn't have gone in had we said 'no, they didn't have weapons of mass destruction,'" Crowley noted.

"I think that's probably right. A great many people would not," Rumsfeld admitted.