Iraq probably destroyed its weapons of mass destruction (WMD) in the early 1990s, the former United Nations chief weapons inspector Hans Blix has said.
Mr Blix hopes Saddam Hussein will tell the truth about WMD
Speaking to the BBC's World Service, Mr Blix said he was more certain than ever that there was no WMD in Iraq.
Mr Blix said the capture of ousted Iraqi leader Saddam Hussein was important, as he may reveal at what stage he might have destroyed them.
The US and UK used concerns over WMD to justify the March invasion of Iraq.
Mr Blix and a team of UN weapons inspectors spent more than three months searching for WMD in Iraq in the build-up to the war without finding anything they deemed significant.
Speaking to the BBC's Newshour programme, Mr Blix said he hoped Saddam Hussein would now reveal the truth about his chemical, biological and nuclear programmes.
"I doubt that he will reveal any WMD, because I think both we UN inspectors and the American inspectors have been looking around and come to the conclusion that there aren't any," Mr Blix said.
"He might be able to reveal when they were done away with. I am inclined to think it was early in 1991 or 1992."
Mr Blix was in the Swedish capital Stockholm on Tuesday to launch an independent international commission on WMD.
He came out of retirement to chair the commission at the request of his native Sweden, which established it following a UN request.
SOME COMMISSION MEMBERS
Former US Defence Secretary
Jordan's Prince El Hassan bin Talal
Chinese General Pan Zhenqiang
A team of 14 commissioners is due to submit proposals by 2005, aimed at reducing the dangers posed by WMD around the world.
He said the end of Saddam Hussein's regime did not mean the end of such threats - and listed North Korea, Iran and the tensions between India and Pakistan as areas of particular concern.
The commission was set up on the initiative of Sweden's late Foreign Minister, Anna Lindh. The Swedish Government will fund its work, but the body will be independent from any government.