In The Unknown Known, Oscar-winning documentarian Errol Morris (The Fog of War) turns his infamous interrotron on former Secretary of Defense Donald Rumsfeld. He was one of the key architects of the U.S. response to the attacks of September 11th under President George W. Bush, which included wars in Iraq and Afghanistan.

The title of Morris’ documentary, out April 4, is taken from a controversial response Rumsfeld gave in February 2002 when, as Secretary of Defense, he was prodded about the lack of evidence concerning “reports” propagated by the Bush administration that Iraq was supplying weapons of mass destruction to terrorist groups:

“Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know that we know. There are known unknowns; that is to say, there are things that we now know we don't know. But there are also unknown unknowns—there are things we do not know we don't know."

In this exclusive clip, Morris grills Rumsfeld about his response to 9/11, in particular why he, along with the rest of the Bush administration, led America to believe that Saddam Hussein was somehow involved in the 9/11 attacks.

“Oh, I don’t think so,” replies Rumsfeld. “It was very clear that the direct planning for 9/11 was done by Osama bin Laden’s people, al Qaeda, and in Afghanistan. I don’t think the American people were confused about that.” Then Morris provides some eye-opening evidence to the contrary.

Watch their showdown here: