From what I recall the intelligence agencies didn't really lie, they had info but it was speculous at best and highly circumstantial.
The runaround that Saddam was doing with UN inspectors was intentional as he thought they had legitimate weaponry. People were just being told to move stuff and not questioning why.
In reality the lying was being done to Saddam, he wanted to build them up but the sanctions were actually working in that they couldn't get the materials but no one was telling him that, they just snowed him for the funding.
The key person that the US evidence was based on was a defector who used the knowledge he had as a negotiation ploy to get out of there. I believe that he knew it was all BS and was afraid he was going to get caught.
The initial push to invade was from DoD as they were still hurt that Afghanistan was a CIA operation not theirs and they had toys they wanted to play with. CIA questioned the validity of the informant but was ignored as being bitter.
At literally the 59th minute of the 11th hour, they finally figured out the guy was lying but then it was too late to save face.