WASHINGTON (NYTIMES) - Attorney General William Barr has said that the United States will not seek the death penalty against two notorious British Islamic State detainees accused of playing a role in the torture and beheadings of Western hostages, potentially clearing the way for Britain to share evidence against them that prosecutors see as crucial to putting them on trial.

The statement, which Barr made in a letter to the British home secretary that the Justice Department released Wednesday (Aug 19), represented a major shift in the Trump administration's policy.

It could open the door to a long-delayed prosecution for the two men, El Shafee Elsheikh and Alexanda Kotey, who were captured by a Kurdish militia in early 2018 and are being held by the US military in Iraq.

"I am writing to provide an assurance that, if the United Kingdom grants our mutual legal assistance request, the United States will not seek the death penalty in any prosecutions it might bring" against the two men, Barr wrote.

He said that if they were somehow nevertheless sentenced to execution, "the death penalty will not be carried out."

At the same time, however, Barr imposed a deadline of Oct 15 for the British government to resolve litigation that has tied up its ability to transfer the evidence.

If it fails to do so by then, he threatened, the United States will instead transfer the two men to the custody of the Iraqi government.

"Time is of the essence," he wrote, adding: "Kotey and Elsheikh are currently held by United States military authorities in an overseas theater of military operations, and it is not tenable to continue holding them there for an extended period. Final decisions must be made about this matter."

Elsheikh and Kotey were half of a cell of four Islamic State Britons who handled hostages - some of whom were eventually beheaded on propaganda videos - and whose victims nicknamed them the Beatles because of their accents.

An early victim was James Foley, an American journalist who was beheaded in 2014.

Diane Foley, his mother, said in an email to The New York Times that the development gave the victims' families hope that the long limbo surrounding whether the two men will ever come to trial may be resolved - although they are also wary about the short deadline.

"We are so hopeful that this assurance will allow the Home Secretary to fully engage with our DOJ and pool all our evidence implicating Kotey and Elsheikh ... just concerned about the tight time frame and legalities around the UK Supreme Court," she wrote.

"But very hopeful and grateful to AG Barr for agreeing to waive the death penalty to allow the UK to share their substantial evidence."

As the Islamic State's so-called caliphate collapsed, the Kurdish-led Syrian Democratic Forces, an American ally, took a large number of its members from around the world into wartime custody.

Many of their home governments have proved reluctant to take them back because of both domestic political reasons and security fears that their own legal systems could result in many of the group's members being released or serving sentences of only a few years.

Kotey and Elsheikh were among them.

The British government sought to strip their citizenship and made clear that it did not want to take them back.

The Trump administration has been willing to prosecute them instead, but the attorney general at the time, Jeff Sessions, opted not to make assurances that the United States would forgo the death penalty - over the objections of four American families whose children were killed by the Islamic State.

Because Britain has abolished the death penalty, such assurances are usually routine when the United States is working with the British criminal justice system.

The British government pressed the Trump administration to provide them again.

But it eventually relented and agreed to hand over the evidence in its possession - and to send officials to testify about it at trial so it would be admissible - if the United States agreed to give the detainees a trial in civilian court rather than sending them to the wartime prison at Guantánamo Bay.

But Elsheikh's mother filed a lawsuit in British court arguing that such sharing of evidence would be illegal, which has indefinitely delayed the transfer, and the issue has been mired in that litigation.

In March, the British Supreme Court preliminarily sided with her and blocked the government from sharing the evidence and providing assistance in the case, although the litigation continues.

The court order means that the British government for now is prevented from transferring the evidence to the United States, notwithstanding its changed stance on the death penalty.

But in a statement, a representative for the home secretary, Priti Patel, suggested a cautious embrace of the development.