Kayla, 26, was kidnapped in Aleppo after having visited a Doctors Without Borders hospital in the war-ravaged city
CAPTIVE US aid worker Kayla Mueller pleads for help in this haunting proof-of-life video sent to her family by her ISIS captors.
The film was sent to her family in Arizona on August 30, 2013 - around 18 months before her death.
Kayla was forced to marry vile ISIS leader Abu Bakr al-Baghdadi who reportedly tortured and constantly raped her before her death in an air strike last year.
In the short video, which was handed to her parents by FBI agents, she says: "My name is Kayla Mueller. I need your help.
"I’ve been here too long, and I’ve been very sick. It’s, it’s very terrifying here."
Mueller, who died last year, was held captive for 18 months by the organisation and kept as a sex slave in a dungeon.
A humanitarian worker from Prescott, Arizona, she had visited a hospital run by Doctors Without Borders, which is also known as Médecins Sans Frontières and MSF before she was kidnapped.
She had been in a vehicle owned by the group on her way from Syria to Turkey when she was abducted.
Earlier this week, in an interview with , her parents Marsha and Carl said the organisation withheld vital information which could have changed Kayla's fate, and ignored pleas to help them get her released.
In a recording made by the couple 10 months after their daughter's disappearance, a senior official from the Doctors Without Borders tells the Muellers: "No... So, the crisis management team that we have installed for our five people and that managed the case for our people will be closed down in the next week... because our case is closed."
Carl admitted to ABC News's 20/20 the organisation makes a difference saying: "They're a fabulous organization, and they do wonderful work."
However, he added: "Somewhere in a boardroom, they decided to leave our daughter there to be tortured and raped and ultimately murdered."
Kayla would have turned 28 this month. She was repeatedly forced to have sex with Abu Bakr al-Baghdadi, the leader of ISIS while she was held captive.
Jason Cone, who is the US executive for the MSF, said the organisation had no obligation to help: "I don't think there was a moral responsibility.
"We can't be in the position of negotiating for people who don't work for us."
He said they did not ask her to go to Syria, and would not have done because she was an American citizen.
Kayla was taken hostage in August 2013 with her boyfriend Omar Alkhani after travelling to the country after he was hired to fix the internet service at a Doctors Without Borders affiliated hospital in Aleppo.
Kayla went because she desperately wanted to do some relief work there.
MSF have released a denying that Kayla was officially working for them.
Alkhani was released after two months, having been beaten, but she was held captive along with two other women who were Kurdish of Yazidi descent.
At least seven Doctors Without Borders staff members were taken hostage and released by the terror group, and the organisation helped negotiate ransom payments.
However it did not include Kayla or speak to the FBI agent involved in the case - which her parents revealed in an email from a senior MSF official.
Three female staff members from MSF were kidnapped in January 2014 were released in April 2014 by the terror group, they had been told to memorize an ISIS email address to give to Kayla's parents.
But it did not get passed on by officials for at least seven weeks, until two male members of its staff were also set free.
