Barr Disavows Death Penalty for Two ISIS ‘Beatles’ if Britain Shares Evidence

Mr. Kotey and Mr. 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 Mr. 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.

The British government’s “priority has always been to protect national security and to deliver justice for the victims and their families,” the statement said. “We continue to work closely with international partners to ensure that those who have committed crimes in the name of Daesh” — another name for the Islamic State — “are brought to justice.”

Mr. Barr’s two-month deadline and threat to send the men to the Iraqi judicial system will now pose a test for not just the British government, but also its independent judiciary. The Iraqi option carries several risks that have previously made American officials see it as unacceptable.

Iraqi courts frequently impose death sentences on Islamic State suspects after trials that last only a few minutes, raising objections about both human rights and failure to take advantage of an opportunity to develop and bring out evidence about what really happened in atrocities. In addition, an Iraqi judge could rule that he has no jurisdiction over the men since it is not clear they ever voluntarily set foot on Iraqi soil, in which case they could be released.