However, they have been shocked to learn that Khibaza has been let out of Abu Ghraib prison and is back on the streets.

'He did not even serve one month of his 10-year sentence,' said Major Moayed Saleh Hashemi, of the major crimes unit. 'We put him in prison and somehow he was released.'

Police say attempts to control a crime wave have been significantly hindered because convicted criminals are being let out of prisons ostensibly controlled by the United States-led occupation authority. According to police, as many as half the criminals jailed since the collapse of Saddam Hussein's regime have been released.

'It's very frustrating,' said Lieutenant Ghassem Ali Hamid, who investigates murders and kidnappings.

'These people are professional criminals. We spend weeks and weeks tracking them down and capturing them. When they release them, it's very hard to capture them again.'

Abu Ghraib is the focus of a prisoner-abuse scandal, in which US troops are accused of abusing Iraqis detained for allegedly taking part in anti-coalition activities.

Coalition officials have been unable to give a clear explanation for the apparent release of criminals like Khibaza.

A US army spokesman, Brigadier-General Mark Kimmitt, said at a recent news conference that many of the released prisoners were 'deemed to no longer be an imminent security threat'.

Meanwhile, Lieutenant-Colonel Barry Johnson, spokesman for US forces at Iraqi prisons, said coalition forces were 'not in a position to release criminal detainees,' as opposed to the so-called security detainees suspected of committing violent acts against US forces.

But he conceded that the coalition had taken charge of criminals while the Ministry of Justice sets up a prison system before the handover of sovereignty on Wednesday.

Lieutenant Hamid cited the case of Habib Obeid Jabala, arrested on a kidnapping charge after police stormed into his house and found a victim bound and gagged last September.

Because of a lack of space at the local police station, officers sent him to Abu Ghraib while they prepared a court case against him.

In March, Lieutenant Hamid spotted Jabala at the police station, trying to get his impounded car out of the police lot.

Jabala told Lieutenant Hamid he was released after his number came up in the dumbela, a lottery to release prisoners.

Colonel Johnson said: 'There is no lottery for releasing detainees being held by any coalition forces.'