When Ali Mufta draped his blanket around the shoulders of a pair of terrified teenage brothers, he thought of it as little more than a touch of kindness in the midst of a situation he describes as "a horror movie". But it was a gesture that saved him from the fate of other prisoners crammed into an underground cell in Sirte, the birthplace of the Libyan dictator, Muammar Gaddafi.

The petrol tanker driver watched horrified as his fellow captives were called out in ones and twos by Gaddafi's soldiers. He listened to their screams and pleas, and saw them return with broken hands and feet, and faces disfigured.

"They removed each person from the room in turn and they beat him and kicked him. They broke fingers and toes. They destroyed the faces. They came back completely covered in blood," he said. "I saw them kick a wounded rebel soldier until he bled to death. I saw a man who was crawling around on all fours as they kicked and beat him, and still he kept crawling. There wasn't a point of his body that wasn't beaten."

Mufta had no reason to believe his fate would be any different. A month ago, the 33-year-old had volunteered to take food to Ras Lanuf, a rebel-held town under attack from Gaddafi's forces. The aid convoy of food trucks and three ambulances from Benghazi arrived only to discover the Libyan dictator's army was already there.

The volunteers were picked up at the hospital, beaten and thrown into a lorry containing the bodies of dead and wounded rebels. "When the lorry was driving, if they saw a body on the road the soldiers went and kicked it in the face to make sure it was dead, and then they drove the lorry over it. This happened three times," he said.

After several hours, Mufta arrived in Sirte, a town of particular ideological as well as strategic significance to the regime.

"They took us inside with the wounded rebels. One was shot in his penis. There was a lot of blood on his trousers. Gaddafi's soldiers recorded it on their phones and were saying dirty words to him. They kept kicking him in the place where he was shot and he died," said Mufta. "After that they tied a rope around his neck and dragged him out saying: get this dog out of here."

Mufta was put in the underground cell with about 28 fellow prisoners, a mixture of rebels and civilians.

"We felt we could relax and sleep because they removed the ties on our hands and the blindfolds. But then every 10 minutes they opened the door and when they find anyone asleep they kicked him in his face. They told us we are al-Qaida and terrorists and we want to destroy the country," he said.

The next morning the two teenage brothers were brought in. "I felt sorry for them so I gave them my place and my blanket. I asked them how they got there. They said they were living in a civilian area of Ras Lanuf and that they didn't leave when Gaddafi's soldiers came. They stayed to protect their mother's house from looting and were captured by soldiers."

In the morning the two boys were taken away and Mufta feared for them. Then his name was called. Outside the cell he was directed through a door. He was terrified.

"I opened the door and there was this small room with some furniture. I found the two brothers from Ras Lanuf sitting there. I was wondering what was going on when they quickly said that I should say what they said," he said. "They told me their uncle was a colonel for internal security and they had other relatives in the security. One of these guys was telling internal security about what was going on in Ras Lanuf with the rebels. He was a spy."

Mufta thinks the army and internal security were too afraid to harm the relatives of a powerful figure in the security apparatus, so the three were released.

His chilling insight into the treatment of people captured by Gaddafi's soldiers is backed by photographs that have emerged in recent days of corpses, apparently captured rebel soldiers, with their hands bound behind them and with their throats slit.

Al-Jazeera obtained video that shows badly beaten young men, with bruised, bloodied and swollen faces, bound and held on a road awaiting transport to prison and an uncertain fate. One was said to have confessed to demonstrating against Gaddafi. Another denied being a rebel.

The footage also shows Gaddafi's soldiers going house to house in the town of Ajdabiya after it briefly fell to government forces, calling on young men to come out. Some emerge with their hands raised. One is waving the green national flag, seen as a symbol of Gaddafi.

Amnesty International says that captured rebel fighters have been found shot in the head with their hands bound behind them. It said that the soldiers appeared to have been executed near Ajdabiya. It called the killings a war crime.

Hundreds more are missing from towns seized by Gaddafi's forces. If they have not been killed, they are likely to be in prison and subjected to torture.

Mufta had a lucky escape, but he was not out of danger. He was in Sirte, Gaddafi's hometown, where anyone from Benghazi was viewed with suspicion. Then came an unusual means of escape.

The regime announced plans for a convoy of "peace buses" with white flags and olive branches to advance towards the front and persuade the revolutionaries to stop fighting. Mufta saw his chance.

He was surprised to see so many other volunteers for the peace mission – four bus loads as it turned out. In time he discovered that, like him, almost everyone on the buses was trying to escape Sirte and get to free Benghazi.

The convoy set off but after some time the driver of Mufta's bus refused to carry on when he saw tanks. The passengers were having none of it. The driver was tossed off the bus and Mufta, with his lorry driving experience, took over.

The bus ploughed on until it eventually crossed the rebel front line, by then about 80km from Sirte, to the astonishment of the suspicious rebels, who wondered if it was some kind of Trojan horse with Gaddafi fighters hidden on board.

Mufta was free but he has not seen any of the people who were in the cell with him return. "What I saw, I never even dreamt it could happen. It's like a horror movie," he said. "Those other prisoners are still in the movie."