The Iraqi defector known as ‘Curveball’ admits he lied about weapons of mass destruction in Iraq but also has no regrets for toppling a dictator despite the deaths, American and Iraqi, his false justification caused.

The 2003 invasion of Iraq was sanctioned largely because of claims the country had weapons of mass destruction (WMDs).

The source of some of the alleged intelligence behind the claims was an Iraqi defector living in Germany, someone who has now admitted the evidence he provided was false.

Now, Colin Powell, disgraced after he testified before the UN with repeating false claims made by Rafid Ahmed Alwan al-Janabi, is calling for an investigation by the Pentagon.

Colin Powell, the US secretary of state at the time of the Iraq invasion, has called on the CIA and Pentagon to explain why they failed to alert him to the unreliability of a key source behind claims of Saddam Hussein’s bio-weapons capability.

Responding to the Guardian’s revelation that the source, Rafid Ahmed Alwan al-Janabi or “Curveball” as his US and German handlers called him, admitted fabricating evidence of Iraq’s secret biological weapons programme, Powell said that questions should be put to the US agencies involved in compiling the case for war.

In particular he singled out the CIA and the Defence Intelligence Agency – the Pentagon’s military intelligence arm. Janabi, an Iraqi defector, was used as the primary source by the Bush administration to justify invading Iraq in March 2003. Doubts about his credibility circulated before the war and have been confirmed by his admission this week that he lied.

Powell said that the CIA and DIA should face questions about why they failed to sound the alarm about Janabi. He demanded to know why it had not been made clear to him that Curveball was totally unreliable before false information was put into the key intelligence assessment, or NIE, put before Congress, into the president’s state of the union address two months before the war and into his own speech to the UN.