My line of questioning was simple: Tell me about the nuclear material you were transporting. His answers also were simple: I wasn’t transporting nuclear material; I didn’t do it. For a while I assumed his tears were a ploy. I applied greater pressure: Stop lying to me; tell me where you got it; we know everything. His crying intensified.

In the famous deck of cards that depicted Hussein’s henchmen, my subject wouldn’t even rank as a two of clubs. The truth is that this old man — caught with car parts patched together to look like a small radioactive-material container — was no more than a con artist. He probably just wanted to make some cash by selling the fake material to a sucker. Almost certainly he was crying in front of me out of genuine despair.

But my questions were unrelenting. I was determined to eke out any details that could offer clues about Al-Zarqawi. A colleague in the tent gave me a confused look, and later commented that my face was indecipherable during the interrogation. My subject protested his innocence and even tried to take my hands in his, pleading for his family’s security. In the end, I turned to the interpreter and whispered, “He doesn’t belong here.” He promised to tell the commanding officer. My comment was as much about the absurdity of the whole situation as it was about the prisoner’s innocence. I had risked the lives of a dozen soldiers to be there — only to find a small-scale confirmation of the ludicrous false premises under which we had invaded and occupied Iraq. The Iraqi weapons of mass destruction were no more than a bit of improvised sham, a con man’s counterfeit goods. In the process I had stumbled into one of the darkest places in wartime Iraq and into the most revealing truth of the conflict: Nobody belonged there.

When I returned to Washington, some weeks later, it was clear to me that people who hadn’t served in Iraq knew little of what was really going on. A friend asked me how the search for weapons of mass destruction was going. I responded wryly, “Well, I’m back, aren’t I?” I avoided explaining the enormity of it. I relied on funny stories of swimming in Uday’s pool or peeing in Hussein’s golden toilets to escape the conversation.

When the Iraq Survey Group’s interim progress report was released, in October 2003, the truth became unavoidable. It offered a thinly veiled admission of failure to find any convincing evidence of recent W.M.D. activity. I had often justified my participation as my duty, but that claim began to sound more and more like an excuse for blind adventurism. It became impossible to square my American sense of free will — our image of ourselves as empowered citizens participating in informed choices — with the reality of the way that we were hoodwinked into going along with the invasion of Iraq. I had been taught throughout my childhood and my military training that America conducts wars based on just cause, but the reality emerging from Iraq was that we had been compelled by deception.

A few months later, in April 2004, CBS News broke the story of torture at Abu Ghraib prison, revealing that American guards, maybe even some of the people whom I had seen at the prison, had beaten and abused prisoners. I was horrified. There had been little to stop me from harming my interviewee there, but doing so would have required moral bankruptcy. The actions of the guards at Abu Ghraib invalidated the American idea of liberation that I believed in. To me, the cruelty and abuse of power represented a perversion of American values.

In that moment, it became clear to me that the administration’s public narrative of the war was exactly what drove us to that dark place. The time-tested tropes of war for freedom and war of liberation had been used masterfully, and had been enabled by false claims of the Hussein regime’s involvement with Al Qaeda. We were fighting in a fantasy and our leaders knew it, even while we were there, yet we persisted.

I was repulsed by the idea that we could have been so easily manipulated. For a time I considered ending my government career. But I also felt that walking away would make me powerless to do anything to push back against the administration’s dishonesty. Instead, I refocused my intelligence career on understanding the underlying causes of war. Later, as an adjunct professor, I spent time developing an assessment of historical false justifications, and taught on the subject. To this day, I’m chastened by the memory of my experience at Abu Ghraib, and I’m haunted by the unknown fate of my interviewee. Like many veterans, I carry a deep desire to prevent another conflict like the invasion of Iraq, fueled by my understanding of the war’s absurdities. But I’m struck by the power of our national momentum toward going to war — especially unnecessary ones — and alarmed that this momentum seems nearly impossible to halt.