I made my plans just before 9/11. I was 19 then and was naïve and did not think war in Afghanistan would have anything to do with Pakistan or my trip there. So I went ahead with my trip.

I was in Pakistan, on a public bus on my way to the airport to return to Germany when the police stopped the bus I was riding in. I was the only non-Pakistani on the bus — some people joke that my reddish hair makes me look Irish — so the police asked me to step off to look at my papers and ask some questions. German journalists told me the same thing happened to them. I was not a journalist, but a tourist, I explained. The police detained me but promised they would soon let me go to the airport. After a few days, the Pakistanis turned me over to American officials. At this point, I was relieved to be in American hands; Americans, I thought, would treat me fairly.

I later learned the United States paid a $3,000 bounty for me. I didn’t know it at the time, but apparently the United States distributed thousands of fliers all over Afghanistan, promising that people who turned over Taliban or Qaeda suspects would, in the words of one flier, get “enough money to take care of your family, your village, your tribe for the rest of your life.” A great number of men wound up in Guantánamo as a result.

I was taken to Kandahar, in Afghanistan, where American interrogators asked me the same questions for several weeks: Where is Osama bin Laden? Was I with Al Qaeda? No, I told them, I was not with Al Qaeda. No, I had no idea where bin Laden was. I begged the interrogators to please call Germany and find out who I was. During their interrogations, they dunked my head under water and punched me in the stomach; they don’t call this waterboarding but it amounts to the same thing. I was sure I would drown.

At one point, I was chained to the ceiling of a building and hung by my hands for days. A doctor sometimes checked if I was O.K.; then I would be strung up again. The pain was unbearable.