My theory always has been that David Kelley had a big hand in the "sexing up" story, and when he was found out...well, we know the rest. Was it that he was mortified to be found out because he didn't think it would get that huge? Or was he simply unable to face the music once he was caught out. My opinion is Kelley was no angel.
As evidence, note that he chose of his own free will to meet surreptitiously with Andrew Gilligan who was well known to have been "reporting" propaganda during the war. Case in point from Gilligan: "The coalition is NOT at Saddam Airport", when in fact our troops certainly were there.
THAT is who Kelley chose to meet with and opine that the government had "sexed up" the dossier.