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One of the excuses that has been put forward is that the Bush administration honestly believed that Iraq had WMD. Reality says otherwise.

In the period before the Iraq war, the CIA and the Bush administration erroneously believed that Saddam Hussein was hiding major programs for weapons of mass destruction. Now NBC News has learned that for a short time the CIA had contact with a secret source at the highest levels within Saddam Hussein’s government, who gave them information far more accurate than what they believed. It is a spy story that has never been told before, and raises new questions about prewar intelligence.

What makes the story significant is the high rank of the source. His name, officials tell NBC News, was Naji Sabri, Iraq’s foreign minister under Saddam. Although Sabri was in Saddam's inner circle, his cosmopolitan ways also helped him fit into diplomatic circles.
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But on that very trip, there was also a secret contact made. The contact was brokered by the French intelligence service, sources say. Intelligence sources say that in a New York hotel room, CIA officers met with an intermediary who represented Sabri. All discussions between Sabri and the CIA were conducted through a "cutout," or third party. Through the intermediary, intelligence sources say, the CIA paid Sabri more than $100,000 in what was, essentially, "good-faith money." And for his part, Sabri, again through the intermediary, relayed information about Saddam’s actual capabilities.

They knew. They lied. Tens of thousands of people have died. Impeach them.