You think maybe Saddam lied to Piro?
The world was aware by that point that the US did not execute prisoners. They interred them forever while trying to extract information. Saddam lied to everyone for his own purposes. In this case Saddam's lie was so simple, Piro wanted to beleived him. By lieing and making it simply obvious, Saddam was hoping to get his interrment extended instead of being handed over to the new Iraq goverment. If Saddam was found hiding in a hole with out his sons, was that a man who wanted to be executed?
Did Piro want to beleive their were no WMD? Have you noticed all of the retired government employees who get in front of the microphone to give information long after the fact, then try to make the reasons for Iraq look like the illusions of a meth addict. What six or 7 firgure job or high fee speaking tour is Piro looking at right now in the public sector that this interview is sealing for him?
Follow the money. Over the next 6 months google Piro and see what he is doing for a living.