°®Âþµº

In this new account of the last days of her life, Mueller was killed by IS operatives because she knew the identities of Baghdadi and his spokesman at the time, Abu Mohammed al-Adnani. 

The new insights into Mueller's death, which were first reported by the New York Times, were told to a former FBI agent working to uncover what happened to Kayla for the Mueller family. 

Umm Sayaf, the wife of a senior IS leader who was killed in a US raid last year, told investigator Ali Soufan that Mueller was moved to various locations at the end of her life, including the house of Baghdadi.

The complete circumstances of Kayla Mueller's death remains unclear, as IS claim she was killed in a Jordanian airstrike while US officials deny the death of civilians in the airstrike.

But Umm Sayaf's comments have given Mueller's family new hope that her remains could be located and brought to the United States.

"I know that Kayla is most likely gone, and in heaven, but what if she isn't?" her mother, Marsha Mueller, said in a recent interview.

"There was always this 1 percent possibility that - could she possibly be alive? We just need to find her and bring her home, that's the goal."

US President Donald Trump called the families of Americans murdered by IS after the October US special forces raid that killed Baghdadi and in his call with the Muellers, promised to help uncover what happened to their daughter.

"The more I learn, the more I can be a part of what happened to Kayla," Mueller said. "That's why I need to know everything. I need to be able to walk part of this with her."

Mueller's parents partnered with Soufan earlier this year to look into Kayla's death and in late July he interviewed Nisreen Assad Ibrahim Bahar, also known as Umm Sayaf.

Umm Sayaf was charged by federal prosecutors in 2016 with holding American Kayla Mueller hostage and with contributing to the aid worker's death.

She admitted after her capture last May that she and her husband kept the 26-year-old Mueller captive along with several other young female hostages, according to an FBI affidavit filed in the case.

Umm Sayaf told Soufyan that Mueller was brought to her house in the Syrian town of Shaddadi in September 2014.

Given a new name "Iman" and encouraged to practice Islam, Mueller was taken away from Umm Sayaf's house by Baghdadi in December 2014 after several Yazidi girls escaped, said Umm Sayaf.

US officials have said that while in custody, Mueller was repeatedly raped by Baghdadi.

'Security issue'

Islamic State announced Mueller's death on Twitter in February 2015, saying she had died in an airstrike.

Umm Sayyaf told Soufyan that a few weeks later her husband told her Mueller had been killed on the orders of Baghdadi and Adnani.

"When she inquired with Abu Sayyaf as to why they would kill her, Abu Sayyaf reluctantly said it was because she knew the identity of al-Adnani and Baghdadi, and this was a security issue for them," Soufan wrote in a summary of the interview obtained by the New York Times.

Umm Sayyaf said Mueller was taken to Baghdadi's house in Raqqa after leaving the house in Shaddadi. Mueller was then kicked out by Baghdadi's oldest wife who assaulted her in a fit of jealousy, a wife of IS media ministry head Abu Hassan told Umm Sayyaf.

Mueller was then taken to Hassan's house, where after ten days she was picked up by Adnani, said Umm Sayaf.

The case against 25-year-old Iraqi Umm Sayyaf was brought one year after Mueller was confirmed dead by the Obama administration, though it's not clear when or if Umm Sayyaf will be brought to the US to stand trial.

Her husband, Abu Sayyaf, a former IS minister for oil and gas, was killed last May in a raid on his compound in Syria by US Special Forces.

'Akin to slavery'

Mueller, from Prescott, Arizona, was taken hostage in August 2013, only days after arriving in Aleppo, Syria, to carry out relief work.

Mueller was transferred in September 2014 along with two Kurdish women of Yazidi descent from an IS prison to the Sayyafs, according to the FBI affidavit.

The affidavit adds that the couple handcuffed the captives, kept them in locked rooms, dictated orders about their activities and movements, and showed them violent IS propaganda videos.

After her capture last year, the affidavit says, Umm Sayyaf admitted she was responsible for Mueller's captivity while her husband traveled on IS business.

She said that al-Baghdadi would occasionally stay at her home and that he "owned" Mueller during those visits, which the FBI says was akin to slavery.

Read more: Retreat and resurgence: IS' never-ending cycle unfolds in Mosul

The Justice Department complaint echoes earlier assertions from US intelligence officials, who had told Mueller's family that their daughter was repeatedly raped by al-Baghdadi.

"The defendant knew how Ms. Mueller was treated by Baghdadi when Ms. Mueller was held against her will in the defendant's home," the affidavit states.

A Yazidi teenager who was held with Mueller and escaped in October 2014 also confirmed the abuse Mueller had suffered at the hands of al-Baghdadi.

Follow us and to stay connected