His arms bore marks of torture – inflicted at the hands of the rebels

Portia Walker in Tripoli sees further evidence of Libya's painful transition

The prisoner's thin arms were the first giveaway. They were pocked with fresh, round scars – the distinctive marks of cigarette burns. Cuts criss-crossed his arms and his left wrist was swollen.

Tortured prisoners are a familiar sight in Libyan jails but the captive at Jdeibah prison in Tripoli was no victim of Colonel Gaddafi's regime, but a prisoner of those who now control the Libyan capital. His wounds serve as a grim warning of the challenges the country faces as it emerges from four decades of institutionalised brutality. The man with the burn marks, Khalid Abdul Jalil Mohammed, 25, served as a soldier in Muammar Gaddafi's army. He was arrested a week ago at a checkpoint in Tripoli and was accused of killing people as he fought for the old regime.

Mr Mohammed hails from the town of Sabha, deep in the southern desert hinterland. It is one of few places in Libya which is still held by forces loyal to the former dictator. He said he joined the army five years ago because he was motivated by a lack of other opportunities. "I was bored," he added. He was paid 532 Libyan dinars a month, which he gave to his family to support his five younger siblings.

The young fighter spent the first part of the war in the east of the country between Ajdabiya and Brega, where Colonel Gaddafi's loyalists battled rebel forces along a front line that shifted backwards and forwards during weeks of fighting. From there, he went to Zawiya, a town near Tripoli in the west which was the scene of some of the fiercest fighting. When rebel forces attacked Zawiya last month, Mr Mohammed's commander told him to surrender. He abandoned his gun and ran away, travelling with a friend to Tripoli where he spent the last month hiding at his friend's house in the suburb of Tajoura.

The guards at the Jdeibah prison insisted that they were not the ones who had tortured him. "I swear – in the prison no one touched him," said one – a 27-year-old man dressed in civilian clothing. Mr Mohammed disagreed, insisting yesterday: "They hurt me here."

However, none of the guards – a trio of 20-something civilian volunteers – denied that their captive had been tortured since he was arrested by rebel forces. "They did it because he was a liar and we couldn't get any information", explained one of them. When Mr Mohammed pulled up the legs of his dirty blue jeans to show the welts and bruises to his calves and bony knees, the guards made me put away my camera and asked me to leave.

Other prisoners interviewed at the compound said they had been treated well and were being fed. During the interviews, prisoners were taken off to be served meals.

Mr Mohammed eventually admitted that he had killed people during fighting on the eastern front. "I was given orders and I had to follow them because I am a soldier," he said. "But I feel guilty now."

Asked what he thought the rebels would do to him, Mr Mohammed looked downcast.

"I will die," he said with bleak resignation. "I killed people. They have to kill me now."