Story highlights Umm Sayyaf, wife of ISIS leader, charged with role in Kayla Mueller's death

Sayaff admitted to forcibly holding female captives with husband in Syria

Captured in 2013, American Kayla Mueller was reported killed last year

(CNN) The widow of a key ISIS leader has been charged as part of a conspiracy that resulted in the death of American hostage Kayla Mueller in February 2015, the U.S. Justice Department said Monday.

Umm Sayyaf, also known as Nasrin As'ad Ibrahim, was captured by U.S. forces in a raid in Deir Ezzor, Syria, in May. She was married to Abu Sayyaf, a senior ISIS operative , who was killed in the same raid in eastern Syria in 2015.

Sayyaf, 25, was charged in federal court on Monday with "conspiring to provide material support to a designated foreign terrorist organization resulting in death," the Justice Department announced.

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Umm and Abu Sayyaf forcibly held Mueller and other female captives in several of their residences after the American was captured in northern Syria in 2013 , according to the indictment. While held in the Sayyaf's home, Mueller and other female 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 criminal complaint said.

Sayyaf was aware of how Mueller was sexually abused by ISIS leader Abu Bakr al-Baghdadi while she was in captivity inside the Sayyafs' home, the Justice Department documents say. U.S. government officials and Mueller's family had been previously aware of Baghdadi's treatment of Mueller while in captivity . According to the documents released Monday, Sayaff admitted Baghdadi "owned" Mueller during her captivity at the Sayyaf residence.

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