THE capture and internment of a leading terror suspect was the only crumb of comfort for relatives of Corporal John Johnston Cosby when he was killed in Iraq just over a year ago.

Now the devastated family has been told that Sajad Abu Aya, whose arrest cost Cosby his life, has been released as a result of a deal to free prisoners prior to the imminent British withdrawal from Basra to a desert airbase outside.

Cosby, 28, described as a “monumental personality” by his men, died commanding a security cordon protecting troops who were in the process of seizing Abu Aya in a northern suburb.

Lieutenant-Colonel Toffer Beattie, commanding officer of the Devon-shire and Dorset Light Infantry, said that Cosby, an expert in covert surveillance, had been “leading from the front and he was putting the success of the mission and the safety of his men before his own”.

His death devastated his family. But it had the consolation of knowing that he had died a soldier’s death and that Abu Aya – a militia leader suspected of several murderous attacks on British forces and Iraqis – was in British hands.

Cosby’s sister Violet, who is planning a skydive this month to raise money for the Army Benevolent Fund in memory of her brother, heard the news from The Sunday Times. “I am speechless,” she said. “We are deeply saddened and upset that we have come to hear this through you and not directly from the Ministry of Defence.”

She said that the family was “incredibly proud” of Cosby: “No one can ever take that from us.”

Abu Aya’s capture was heralded as a coup at the time. Major Charlie Burbridge, a British military spokesman, said: “We got the man we wanted. He was strongly suspected of involvement in planning and directing terrorist attacks on civilians in Basra, executions and attacks on coalition forces.”

Yesterday Major Mike Shearer, a spokesman in Basra, said it would be in breach of international laws to discuss details of prisoners with anyone other than the International Red Cross. But he was able to confirm that “internees are regularly released as part of the routine review of cases”.

He added: “Whenever possible and appropriate, internees are transferred to the Iraqi criminal justice system for prosecution or are released when the grounds for internment no longer exist.”

A Ministry of Defence statement said the British were currently holding 88 people. But British forces have reportedly struck a deal to release prisoners in what some Iraqi officials say is a necessary concession to secure their safe departure.

Last week an Iraqi security official told an American newspaper that an agreement between British and Iraqi authorities had resulted in the transfer of more than two dozen Mahdi Army prisoners to Iraqi custody.

The official said they were then released by an Iraqi court to pacify the Shi’ite militia of Moqtada al-Sadr, the radical cleric, during the imminent and highly symbolic handover to the Iraqis of Basra Palace, the last British bastion in the city.

Abu Aya was a member of the Mahdi Army, which has been responsible for most of the British and Iraqi casualties in southern areas. Cosby was the 114th British soldier to die in Iraq.

Iraqi officials said that after receiving Abu Aya from the British, the judicial authorities had freed him on the grounds of insufficient evidence. “He is now at home, a free man,” one said.

Yesterday a detailed account of the prisoner release deal came from the British lawyer representing another internee. Phil Shiner, of Public Interest Lawyers, represents Ali al-Jedda,a British national of Iraqi origin, who was detained by American forces in Baghdad in 2004 and handed over to the British. The father of six has been interned ever since without charge.

He denies that there are any grounds for his imprisonment and is seeking a judicial review of his case. The House of Lords is due to hear his application in October.

Shiner said Jedda had told him the British were negotiating directly with one of his fellow prisoners over who should be released. Meetings had been held between the prisoner coordinating the deal and Major-General Jonathan Shaw, Britain’s most senior officer in Basra, in July and August, he said.

The first meeting to secure the prisoners’ release had taken place between the prisoner and a Foreign Office official in March.

On Friday, Jedda said the Mahdi Army had demanded that very day the release of three more of its men. “These men are wanted by the US and difficult to release but they are now due to be released on September 13,” he said. “These people are murderers and known in the prison as ‘the group of the dead’.”

He added: “The militia behind the deal want the British out of Basra and out of Iraq. General Mohan, of the Iraqi government, asked the British not to leave the palace in Basra because, if they do, the militia will move in and take over. The person behind the deal said no, the British must leave in five days. They are due to leave in two or three days’ time.” Mohan is the military commander of southeastern Iraq.

Both American and Iraqi officials fear the British withdrawal from Basra will leave the city in chaos with rival militias fighting for control.

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