Former CIA analyst John Nixon was tasked with questioning the Iraqi dictator after he was found hiding in a cave in December 2003.
But talking to Hussein, his advisers and subsequent research had led him to the conclusion that Iraq's nuclear weapons programme had ended years earlier.
His team were regarded as “failures” after they came to that conclusion, he told the BBC,
Mr Nixon added that he was not invited to debrief the then president George W Bush until 2008 - two years after Hussein's execution.
In a scathing assessment of the former Commander in Chief, he said he was one of the few to shake both Mr Bush's hand and that of Hussein, but he would rather have spent more time with the latter.
Mr Bush was “isolated from reality” and his advisors were yes men, he said.
“I used to think what we said at the CIA mattered and the president would listen, but it doesn't matter what we say, politics trumps intelligence”, he added.
Mr Nixon, who left the CIA in 2011, said he was “ashamed” of what happened in Iraq after Hussein’s fall.
He said the Bush Administration gave no thought to what would happen after the US led invasion of the country.
Perhaps, in light of the subsequent rise of Isis, the region would have been better off if Hussein had remained in his post, he added.
Mr Nixon's comments come after the Chilcot Report finally delivered its verdict on Tony Blair’s decision to take Britain into the war alongside the US.
Sir John Chilcot savaged the decision to go to war and said there was “no imminent threat from Saddam Hussein” in March 2003.
He said: “We have concluded that the UK chose to join the invasion of Iraq before the peaceful options for disarmament had been exhausted. Military action at that time was not a last resort.”
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