The US inspector sent on an unsuccessful mission to find Weapons of Mass Destruction (WMD) in Iraq has said intelligence about Saddam Hussein's munitions was deeply flawed.
But Mr David Kay told Congress he did not believe the information was not deliberately distorted.
He resigned his post a chief weapons inspector last week after saying he found no evidence that Iraq had chemical or biological stockpiles.
Under questioning by Senate Democrats in Washington, Mr Kay also offered doubts about Bush administration claims that trailers and aluminium tubes were intended for weapons of mass destruction.
He said the UN inspections - which were criticised in the lead up to the US-led attack - "achieved quite a bit". But he agreed with Republican senators that there was no doubt deposed Saddam had ambitions to acquire and use WMD.
Saddam had secret weapons development programmes that violated UN resolutions and the world is safer now he has been deposed, he told Congress. "I have said I actually think this may be one of those cases where it was even more dangerous than we thought," he told the Senate Armed Services Committee.
President Bush's public rationale for going to war was based mostly on claims that Iraq's stockpile of weapons posed a clear threat to the United States and others.
Mr Kay said he believed an outside inquiry would be important to see why intelligence failed and how it could be improved. He also indicated there is a "theoretical possibility" that banned weapons could still turn up somewhere in Iraq.
AP