Doctors Without Borders had no ‘moral responsibility’ to help ISIS hostage Kayla Mueller

WATCH ABOVE: Coverage of the death of U.S. aid worker Kayla Mueller in Feb. 2015.

The parents of U.S. aid worker Kayla Mueller, who was killed in early 2015 after being held hostage by the so-called Islamic State, have revealed the international aid agency Doctors Without Borders refused their request to help negotiate their daughter’s release.

Marsha and Carl Mueller released a recording to ABC News of a telephone conversation they had with the humanitarian organization 10 months after ISIS militants kidnapped their daughter in Syria, on Aug. 4, 2013.

READ MORE: Who is Kayla Jean Mueller? Read the ISIS captive’s letter to family

Although the Muellers praised the work of Doctors Without Borders, also referred to by its French acronym, MSF, the Arizona parents said the group turned its back on helping their 26-year-old daughter.

“… Somewhere in a boardroom, they decided to leave our daughter there to be tortured and raped and ultimately murdered,” Carl Mueller told ABC News for a documentary airing on 20/20 Friday night.

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In the recorded phone call, an official with the organization told Kayla’s parents the case was closed after securing the release of five of its own staff.

WATCH: Kayla Mueller heartbroken after confirming daughter killed in Syria

Why didn’t MSF help Kayla Mueller?

Mueller wasn’t a volunteer or staff member for MSF — she had been working with another organization, Support to Life — but she was travelling in an MSF-marked vehicle when she was kidnapped in Aleppo.

She was travelling to a bus depot, to head back to her home base in Turkey, with her boyfriend, Omar Alkhani. He had been hired to repair Internet equipment at an MSF hospital in Aleppo. Mueller tagged along to see the humanitarian situation with her own eyes.

ISIS captors released Alkhani after beating and interrogating him for 20 days. He told The Associated Press, after her death in February 2015, he saw her briefly before he was set free.

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READ MORE: More female extremists leaving Canada to join Islamic State: report

MSF-USA executive director, Jason Cone, told ABC News the organization didn’t have “a moral responsibility” to negotiate with the terror group for her release, even though it helped broker the release of five of its staff with whom Mueller had also been held.

“We can’t be in the business of negotiating for people who don’t work for us,” Cone told ABC News in an interview for the documentary.”

In a statement released Wednesday, ahead of the 20/20 broadcast, MSF further defended its actions, saying the organization would never have allowed Mueller to visit its facility had it been given prior knowledge of her plans.

MSF explained U.S. citizens were prohibited from even working at its facilities in Syria due to the high security risk to Western civilians, in particular Americans.

Mueller was one of several U.S. and European hostages ISIS held for ransom, once a major source of its funding.

Mueller’s death followed a string of gruesome beheadings of U.S., British and Japanese journalists and aid workers, beginning with American freelance journalist James Foley in August 2014, after their respective governments refused to meet ransom demands.

In response to Mueller’s death and the executions of Foley, fellow American journalist Steven Sotloff and aid worker Abdul-Rahman (Peter) Kassig, the U.S. government lightened its policy on ransom payments to allow families to negotiate with terror groups without fear of prosecution.

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WATCH: President Barack Obama softened U.S. policy on cash for hostages

ABC News also spoke with several former ISIS hostages who gave insight into Mueller’s time in captivity, describing how she had the strength to stand up to her captors.

The exact circumstances in which Mueller died are unknown, but it was revealed after her death she had been tortured and raped by her captors — including, reportedly, by ISIS leader Abu Bakr al-Baghdadi.

No negotiations for nearly a year

Mueller’s parents also provided ABC News with a 10-second “proof of life” video they received a month after she was first taken captive.

“I need your help. I’ve been here too long and I’ve been very sick, and it’s very terrifying here,” Mueller said, wearing a black scarf around her head.

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“I saw how thin she looked, but I saw that her eyes were very clear and steady,” Marsha Mueller told ABC News. “It broke my heart, but I also saw her strength.”

But it wasn’t until the following May that Muellers could even attempt to negotiate for their only daughter’s release.

That was after MSF provided the Muellers with an email address for an ISIS contact, which the organization provided after all of its captive staff had been freed.

MSF, in its statement Wednesday, expressed remorse for not sharing the information sooner.

“We regret the fact that Marsha Mueller had to reach out to us first before we did so; we should have reached out to the family first, and we have apologized to the Mueller’s for that.”

Within days of contacting ISIS, the Muellers received another proof of life recording of their daughter. In the audio clip, she explained the terror group’s demands.

“Mom and Dad, I still am remaining healthy. You should have already received the three answers to the proof of life questions you provided. Those detaining me are demanding an exchange of Dr. Aafia Siddiqui’s release for my release. If this is not achievable, they are demanding 5 million euros to ensure my release,” ABC News reported Mueller as saying in the recording.

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According to ABC News, the clip ended with Mueller saying “Goodbye” to her parents.

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