Kayla Mueller is shown after speaking to a group in Prescott, Ariz., in May 2013. The Islamic State claimed she was killed after a Jordanian fighter jet dropped a bomb on the building where she was being held captive in Syria. (Jo. L. Keener/Daily Courier via Associated Press)

Federal prosecutors filed a criminal charge Monday against an Iraqi woman accused of taking hostage an American aid worker who was killed last year in Syria.

The Iraqi woman, known as Umm Sayyaf or Nisreen Assad Ibrahim Bahar, was captured in May in a U.S. commando raid in eastern Syria. Her husband, a senior Islamic State official, was killed in the assault.

Sayyaf was charged in federal court in Alexandria, Va., with conspiring to provide material support to a designated foreign terrorist organization resulting in death. Justice Department officials and federal prosecutors had been debating charges­ in the case for months.

Authorities allege that Sayyaf played a role in the imprisonment of Kayla Mueller, 26, of Prescott, Ariz., who was repeatedly abused and raped by the leader of the Islamic State. Mueller, who was abducted in 2013 in the Syrian city of Aleppo, had traveled to the region to help refugees trying to escape the civil war.

[Kayla Mueller, American hostage of the Islamic State, confirmed dead]

After Sayyaf’s capture, she was taken to a U.S. air base near the Iraqi Kurdish city of Irbil, where the FBI-led High-Value Detainee Interrogation Group questioned her for intelligence purposes. Then FBI agents from the Washington Field Office, known as a clean team, interviewed her repeatedly, working to build a criminal case against her for a future prosecution in federal court.

According to an affidavit by FBI Special Agent William H. Heaney, Sayyaf admitted that she and her husband were responsible for maintaining custody of Mueller and other captives, and that she thought Mueller was being held for ransom or some type of prisoner exchange. Sayyaf also admitted, according to the affidavit, that her home was used to store large amounts of cash that the Islamic State had made through its oil and gas businesses and that Abu Bakr al-Baghdadi, the leader of the Islamic State, and other terrorists sometimes stayed there. It also apparently was used to store firearms, according to the affidavit.

The Iraqis took custody of Sayyaf in August, and it is unlikely that she will ever be transported to the United States. Still, federal prosecutors and FBI agents felt that charges in the case might bring some measure of comfort to Mueller’s family, officials said.

There also were concerns, officials said, that Sayyaf could eventually be released in a prisoner exchange. The federal charge will allow the FBI to arrest her should that happen.

The Islamic State claimed in February that Mueller was killed after a Jordanian fighter jet dropped a bomb on the building where she was being held. The terrorist group sent photographs of the dead woman to her family. U.S. intelligence officials have said they still do not know how she died.

The charge revealed some new information about Mueller’s time in captivity. According to the affidavit, she was moved from an Islamic State prison to Sayyaf and her husband’s custody about Sept. 24, 2014.

Mueller and other captives were at times handcuffed or kept in locked rooms, chastised by Sayyaf as “kafir” or “infidels,” according to the affidavit. The affidavit alleges that Mueller was shown violent Islamic State propaganda videos and raped by Baghdadi.

Mueller’s exact whereabouts in captivity remain murky because she was moved several times and always a step ahead of U.S. intelligence. Officials said she was being held for months with other American and Western hostages in Raqqa, the group’s de facto capital in Syria. In late June 2014, the United States confirmed their location. Delta Force commandos launched a raid the next month, but she and the others were gone.

U.S. intelligence later learned that Mueller was taken to another location, where she lived with Sayyaf and her husband along with a pair of Yazidi women who escaped in October 2014.

A U.S. intelligence official said they did not locate the house until late 2014 or early 2015. “It took a while to figure out the Yazidi story,” the official said.

U.S. intelligence watched the house for any signs of Mueller, Sayyaf, her husband or Baghdadi. Officials said FBI and Delta Force commandoes prepared to raid the house and devised a plan to collect evidence, according to one of the intelligence officials.

But Mueller and the others never returned, and the United States called off the raid. Officials said they are not sure where Mueller was taken after the Yazidi women escaped but suspect that she spent her last months alive near Raqqa, where she was killed about this time last year.

Sayyaf was eventually captured at a house in eastern Syria that her husband, Fathi ben Awn ben Jildi Murad al-Tunisi, a Tunisian known as Abu Sayyaf, used for his illicit oil business. Officials said that Delta Force commandoes and members of the FBI’s elite Hostage Rescue Team recovered a gold mine in intelligence after that raid, in which Abu Sayyaf was killed.

Umm Sayyaf told investigators that her family members belonged to the terrorist group that preceded the Islamic State and that she married her husband in 2010 while he was a member of that group.