Wife of ISIS Figure Charged in American Woman Kayla Mueller's Death

— -- The U.S. Department of Justice today charge the wife of a top ISIS leader today for her alleged role in a “conspiracy” that led to the death of American aid worker Kayla Mueller, who was reported killed in Syria a year ago.

It was unclear Monday night whether the U.S. was expecting to take custody of Nasrin As'ad Ibrahim, known as "Umm Sayyaf.” American forces had originally captured Sayyaf in a May 2015 raid that killed her husband, ISIS oil and gas “emir” Abu Sayyaf, but Umm Sayyaf was handed over to the Kurdish government in northern Iraq last August.

An FBI affidavit against Umm Sayyaf described how Mueller was kept by the Sayyafs on behalf of ISIS leader Abu Bakr al-Baghdadi, who raped her repeatedly, as ABC News previously reported. Umm Sayyaf was the “sole” person responsible for Mueller while in captivity, the Justice Department said.

“The captives were at various times handcuffed, held in locked rooms, and given orders on a daily basis with respect to their activities, movements and liberty,” the FBI affidavit said. “While in captivity, Kayla Jean Mueller was sexually abused by [al-]Baghdadi, who forced her to have sex with him.”

The Justice Department said Umm Sayyaf would personally threaten Mueller and Yazidi teenage girls, who were also being held, "telling them that she would kill them if they did not listen to her."

Mueller, 26, of Prescott, Arizona, was a committed humanitarian aid worker captured in Aleppo, Syria, and held for 17 months as a hostage with other Westerners. In the Fall of 2014, she was personally selected by ISIS "Caliph" Abu Bakr al-Baghdadi to be his personal hostage against her will, family and counter-terrorism sources have said.

"We were told Kayla was tortured, that she was the property of al-Baghdadi. We were told that in June by the government," Mueller’s mother, Marsha, told ABC News in 2015.

The Justice Department today alleged that Umm Sayyaf has admitted to the FBI that al-Baghdadi “owned” Mueller during her captivity at the Sayyaf compound and "admitted that 'owning' is equivalent to slavery."

The Mueller family has been stung by media reports which suggested -- they believe falsely -- their only daughter naively allowed herself to be captured and then subsequently passed up opportunities to escape from the clutches of her ISIS captors. All evidence is to the contrary, according to her family and many U.S. officials and private hostage negotiators familiar with details of her case.

Mueller was captured in a vehicle on a road in Aleppo, which the humanitarian medical group Medicines San Frontiers (Doctors Without Borders) has said happened while she was traveling with several of their staff, one of whom was an MSF contractor who had asked her to assist him in a trip to an MSF hospital.

The MSF contractor later tried to rescue her by telling ISIS she was his wife -- but Mueller had already told the terrorists holding her that she was not married and feared the consequences of lying to them, another close confidante of Kayla's told ABC News.

Mueller was held captive with, but at times segregated from, a group of American, British and European hostages held at an old oil refinery site south of ISIS's de facto capital of Raqqa, Syria.

The U.S. Army’s elite unit Delta Force attempted a rescue mission in the area in July 2014 but the hostages had been moved just days before the counter-terror squad moved in, U.S. officials said.

Instead, one by one, the western hostages were beheaded beginning in August on video by ISIS "executioner" Mohammed Emwazi, dubbed "Jihadi John." But Kayla Mueller was never shown on video or publicly threatened.

Privately, ISIS emailed threats to execute Mueller if her family didn't pay millions in euros for her, as ABC News reported in August 2014. Many European hostages had been ransomed successfully but the U.S. and United Kingdom steadfastly refused to allow ransom payments for their citizens and their executions became a political tool for ISIS, which said the journalists and aid workers were being decapitated because of the West's bombing campaign in Iraq and Syria.

In January 2015, two counter-terrorism officials told ABC News that a credible sighting of Mueller had come to the attention of the U.S. Joint Special Operations Command the previous October. It was Yazidi girls who had escaped the Sayyaf household, including one former ISIS slave with what was described as a photographic memory, who had considered her friend Kayla Mueller as a big sister and protector of the girls. Military officials began to hunt Abu Sayyaf in earnest, with many hoping a ground force operation by Delta to rescue her could be mounted if he was found.

ISIS continued to execute its hostages, including two Japanese friends and a Jordanian fighter pilot shown burned alive in a grisly video. Jordan immediately retaliated by executing a female terrorist bomber who ISIS had demanded be released.

Then, in February 2015, ISIS claimed Mueller had been accidentally killed by a Jordanian airstrike. U.S. officials confirmed Mueller’s death, but denied that there had even been any Jordanian airstrikes that day.

Some U.S. officials vowed to find Abu Sayyaf and bring him to justice in a lower Manhattan federal court where many terrorists have been tried and convicted.

That opportunity finally came for Delta on May 15 in a ground force operation against a house in Syria, the White House said in an announcement afterward. As Sayyaf's guards tried to hide from the American commandos, they all were killed. The Delta operators then killed Abu Sayyaf "when he engaged U.S. forces," Defense Secretary Ash Carter said.

Umm Sayyaf was captured alive and one Yazidi girl was rescued. The wife of the Tunisian senior ISIS leader was grilled for weeks by the FBI-led High Value Interrogation Group and she quickly confirmed that Mueller had been held prisoner in their household for Baghdadi, who had raped her, counter-terrorism sources told ABC News. Some intelligence prior to Umm Sayyaf's interrogation had assessed that Abu Sayyaf held her and had taken the American hostage as his own forced "wife," but it became apparent that he had actually kept her as a captive for his leader.

Last August, the U.S. turned Umm Sayyaf over to the Iraqi Kurdistan Regional Government’s Ministry of Interior, the Defense Department announced. "The decision to transfer Umm Sayyaf to the Iraqi government was based on the U.S. government determination that the detainee’s transfer would be appropriate with respect to legal, diplomatic, intelligence, security, and law enforcement considerations," the DOD statement said.

“The charges filed today allege that Umm Sayyaf and others conspired to provide material support to ISIL and that this conspiracy resulted in the death of Kayla Jean Mueller,” Assistant Attorney General Carlin said in a statement today. “Sayyaf is currently in Iraqi custody for her terrorism-related activities. We fully support the Iraqi prosecution of Sayyaf and will continue to work with the authorities there to pursue our shared goal of holding Sayyaf accountable for her crimes. At the same time, these charges reflect that the U.S. justice system remains a powerful tool to bring to bear against those who harm our citizens abroad. We will continue to pursue justice for Kayla and for all American victims of terrorism.”