Mueller died this past February in an airstrike carried out by the Jordanian army.
The allegations came from both officials in counter terrorism and the aid worker’s family.
Mueller, who was 26 and from Prescott, Arizona, was captured while working in Syria during 2013 in the city of Aleppo.
Al-Baghdadi brought Mueller with him to the home of Tunisian Abu Sayyaf who was in charge of the gas and oil revenue for the organization said officials in counter terrorism.
Details of how Mueller was treated initially came from a group of Yazidi girls who had also been held at the same house. One was 14 years old who escaped in August of 2014. The version by the teens was corroborated by officials from the U.S.
The teen who escaped was able to reach Kurdistan in Iraq where she spoke with commandos from the U.S. in November of 2014. Intelligence agencies were able to corroborate her accounts and officials from the U.S. then passed that information on to the Mueller family this past June.
Umm Sayyaf the widow of Abuy Sayyaf who was killed in a raid by the U.S. also gave information about Mueller as well as information about the terrorist group itself.
The Yazidi girls’ accounts included telling officials that a number of Yazidi women had come and gone from the Sayyaf house. The women left the Sayyaf home and were taken to be given to the IS fighters as presents.
During a lengthy interrogation by Americans in Iraq, Sayyaf’s widow said that Kayla was owned by al-Baghdadi.
When the Yazidi girl made her escape with one of her sister’s she had asked Mueller to come with her, Mueller’s parents were told, but Kayla had refused as she worried that her Western appearance could lead to them being captured.