The new head of the US team searching for banned weapons in Iraq says he has been instructed simply to find "the truth, wherever that lay".
Mr Duelfer was involved in checking Iraq's disarmament in the 1990s
Charles Duelfer said recently he did not believe Iraq had weapons of mass destruction, but he insists he will approach his new job with an open mind.
Senior officials in the US and UK say weapons programmes - the key reason for invading Iraq - may still be found.
David Kay, who quit as head of the US search, said he thinks there are none.
Mr Kay's resignation from the Iraq Survey Group had been expected, but his strong comments had not.
In an interview with Reuters news agency, Mr Kay said he did not believe there had been large-scale production of chemical or biological weapons in Iraq since the end of the first Gulf War in 1991.
"I don't think they existed," Mr Kay said.
"What everyone was talking about is stockpiles produced after the end of the last Gulf War and I don't think there was a large-scale production programme in the 90s."
Mr Duelfer, a 51 year-old former UN weapons inspector, distanced himself from comments earlier this month that he did not believe banned weapons would ever be found. He said he had held that view as an outsider.
"I have now been given the responsibility of being in charge of the investigation and I don't know what the outcome will be.
"I don't want to pre-judge that," he said, adding that Central Intelligence Agency Director George Tenet told him to find only one thing: "That is the truth, wherever that lay".
No WMDs have been found in Iraq
Both Washington and London have modified their pre-war stance to say the search is for evidence of weapons of mass destruction (WMD) programmes - not necessarily the arms themselves.
In his State of the Union address, US President George W Bush reiterated his view that the war to overthrow Saddam Hussein had been necessary or "the dictator's weapons of mass destruction programmes would continue to this day".
White House spokesman Scott McClellan stuck to that view: "We remain confident that the Iraq Survey Group will uncover the truth about Saddam Hussein's regime, the regime's weapons of destruction programmes."
A spokesman for UK Prime Minister Tony Blair echoed him, saying: "It is important people are patient and we let the Iraq Survey Group do its work.
"There is still more work to be done and we await the findings of that. But our position is unchanged."
'Nowhere to hide'
A former UN weapons inspector who opposed the war, Scott Ritter, told the BBC that while Iraq was a large country, there were only limited places to look for weapons factories.
"Weapons of mass destruction are not produced in the deserts of Iraq or in the mountains of Iraq. They are produced in modern industrial facilities," he said.
Mr Kay led the Iraq Survey Group from June 2003
"They have been forensically examined and no evidence of weapons of mass destruction manufacture has been discovered. You cannot hide a weapon unless you've produced it first."
Mr Kay's comments are being used by opponents of Mr Bush, who see the war in Iraq as one area where he may face difficulties in November's presidential election.
"It increasingly appears that our intelligence was wrong about Iraq's weapons, and the administration compounded that mistake by exaggerating the nuclear threat and Iraq's ties to al-Qaeda," said John Rockefeller, the senior Democrat on the Senate Intelligence Committee.
"As a result, the United States is paying a very heavy price."