He came to my shop around 10.30am. You could tell straight away that he had just been released. His face was bruised all over. His teeth were broken and he could hardly open his eyes.

He was not even into politics. He was just an ordinary 18-year-old in the last year of school. Before the election he came to me and asked how he should vote. He looks up to me. His father is an Ahmadinejad supporter.

He had gone home directly after his release, but his father did not let him in. He didn't mention he had been raped. At first, he didn't tell me either. It was the doctor who first noticed it and told me.

When he came to my shop he collapsed in a chair. He said he had nowhere to go and asked if he could stay with me. I called a friend of mine who is a doctor to come home and see him. Then I brought him home.

His shoulder blades and arms were wounded. There were some slashes on the face. No bone fractures, but he was bruised all over the body. I wanted to take some photos but he did not let me. The doctor said only four of his teeth were intact, the rest were broken. You could hardly understand what he said.

Then the doctor told me what had happened. He had suffered rupture of the rectum and the doctor feared colonic bleeding. He suggested we take him to the hospital immediately.

They registered him under a false name and with somebody else's insurance. The nurses were crying. Two of them asked what sort of beast had beaten him up like that. He was a broken man. He told us not to waste our money on him, and that he would kill himself.

He was arrested in Shiraz on 15 June, the Monday after the election. Some sturdy young men made a human shield around the demonstrators. He was among them. He said he managed to hit some of the anti-riot police. But then they caught him and beat him up.

"I was kept in a van till evening that day and then transferred to a solitary cell where I was kept for two days," he said. "Then I was repeatedly interrogated, beaten and hung from a ceiling. They call it chicken kebab. They tie your hands and feet together and hang you from the ceiling, turning you around and beating you with cables.

"They gave us warm water to drink and one meal a day. Repeated smacking was a regular punishment. In interrogations, they kept on asking if I was instructed from abroad. I believed I was going to be sent from the detention centre to prison. But they sent me to where they called Roughnecks' Room. There were some other youths of my age in there. I asked a guard why I am not sent to prison and the reply was: 'You have to be our guest for a while.'

"I refused to confess during interrogations. They said: 'Ask your friends what we'll do to you if you don't co-operate.' Others in the room were also arrested on 15 June. I was tempted to confess at this point but I didn't. On the third and fourth day, they beat me up again. They insisted we were instructed from abroad. I kept on saying we were only protesting for our votes.

"It was on Saturday or Sunday that they raped me for the first time. There were three or four huge guys we had not seen before. They came to me and tore my clothes. I tried to resist but two of them laid me on the floor and the third did it. It was done in front of four other detainees.

"My cell mates, especially the older one, tried to console me. They said nobody loses his dignity through such an act. They did it to two other cell mates in the next days. Then it became a routine. We were so weak and beaten up that could not do anything.

"Then the interrogations started again. They said: 'If you don't come to your senses we will send you to Adel Abad [another prison in Shiraz] to the pederasts' section so that you receive such treatment every day.' I was so weak I did not know what to say. Then they asked for my contacts. I told them I had no contacts and I was informed about the demonstrations through the internet.

"The same routine was continued till this morning when I was released. In the last week, there was no interrogation, no beating. Only rape and solitary confinement."

This is what he recounted. But he couldn't articulate quite like this. He was in much physical and mental pain as he talked. I asked him to tell his story in the hope of making a difference to those still detained.

• Esfandiar Poorgiv is a pseudonym.