The police station where the men were held recorded that they had been handed over to an American military police lieutenant for transfer to the US-run Camp Cuervo detention centre. But an American military spokesman told the IoS that there was no record of the two prisoners in their database.

"The Americans are allowing the breakdown of Iraqi society because they are only interested in fighting the insurgency," said a senior Iraqi police officer. "We are dealing with an epidemic of kidnapping, extortion and violent crime, but even though we know the Americans monitor calls on mobiles and satellite phones, which are often used in ransom negotiations, they will not pass on any criminal intelligence to us. They only want to use the information against insurgents."

An Iraqi government source confirmed that criminal suspects were often released if they agreed to inform on insurgents, despite the dangers to ordinary Iraqis. The Iraqi middle class has been heavily targeted by kidnappers since the fall of Saddam Hussein. Many doctors, a favourite target, and businessmen have fled to Syria, Jordan and Egypt. The police admit that they have been unable to do anything to stop the wave of abductions.

Dr Thamir Mohammed Ali Hasafa al-Kaisey, 60, a GP, was seized by a gang of 11 kidnappers in three cars as he drove home from his clinic in Baghdad at 6.30pm on 23 December. "I was 50 metres from my house when men with guns in a Jeep Cherokee stopped me and beat me with their fists," Dr Hasafa later told police. "They put me in their car with my face on the ground and tied me up with my own jacket."

Although kidnappers operate with near impunity in central Iraq, Dr Hasafa had an extraordinary stroke of luck. His captors ran into a police checkpoint, and shooting broke out. Even though his leg was broken in the beating, the doctor was able to crawl out of the back of the car and shout to the police: "I am a doctor and I was kidnapped."

The case was a rare breakthough for the police. In their confessions, obtained by the IoS, the two suspects - one a serving police lieutenant - give a unique picture of how the gangs work, and the extraordinarily high number of kidnappings they carry out.

Mohammed Najim Abdullah al-Dhouri, the police lieutenant, and Adnan Ashur Ali al-Jabouri are both members of powerful tribes from which Saddam drew many of his inner circle of security men and army officers. But the motive of the gang seemed to have been purely criminal.

Adnan Ashur told the investigating judge that the leaders of the gang were Eyhab, nicknamed Abu Fahad, who ran a mobile phone shop, and his brother, Hisham. Eyhab, he said, was a criminal sentenced to 40 years in jail by the old regime. He had apparently been freed during a general amnesty by Saddam at the end of 2002.

Mohammed Najim, who was based in Sadr City in east Baghdad, lived in special police housing. He said: "I was involved with Hisham prior to the fall of Saddam. Later he approached me about kidnapping prominent men. My task was to provide security for the gang." All the gang members were armed with pistols. They had safe houses in which to keep kidnap victims. Both suspects said they had taken part in numerous other kidnappings in the previous few months, with their victims paying up to $60,000 (£31,000) each. Ironically, the informant who had told them that Dr Hasafa was worth kidnapping was a guard hired by householders to protect the street where he lived.

The Iraqi police were jubilant that they finally had detailed information on how a kidnap gang operated. The two captured men were willing to provide the names and addresses of other gang members, and the success was lauded by Iraqi television and the local press. To the consternation of the police, however, on 30 December a convoy of US military police arrived at al-Khansa police station, where Mohammed Najim and Adnan Ashur were being held. The Iraqi police officer at the station recorded: "They have requested the custody of the two assailants." Iraqi police dropped the case against the rest of the gang.

Dr Hasafa, meanwhile, received two visits from the families of the prisoners. The first was from the father of Mohammed Najim, who offered money if the kidnap charge was withdrawn. He said he had been an officer in the Republican Guard and added menacingly: "You know what we are capable of doing."

During the second meeting Dr Hasafa learned that his kidnappers had been freed. He refused to withdraw charges, despite death threats to his family, but in January he fled to Jordan and then Egypt.