The parents of American aid worker Peter Kassig who has been captured by ISIS have revealed they have been sent a horrifying audio recording of their son begging for his life. Ed and Paula Kassig, from Indianapolis, said it was the first time they have heard the 26-year-old's voice in over a year and he sounded 'like a robot.' The couple, were ordered by ISIS to keep his capture a secret, but when his picture surfaced on TV days ago, they decided to speak out in hopes their son will hear their words. SCROLL DOWN FOR VIDEOS . Plea: Ed and Paula Kassig, from Indianapolis, the parents of American aid worker Peter Kassig who has been captured by ISIS, have revealed have been sent a horrifying audio recording of their son begging for his life . Ed and Paula Kassig, from Indianapolis, said it was the first time they have heard the 26-year-old's voice in over a year and he sounded 'like a robot' In the audio recording Peter said his life was in jeopardy if U.S. airstrikes did not stop . Sitting in their living room with a school photo of Peter - also known by the Islamic name Abdul-Rahman in the background, Mr Kassig told CBS: 'The dynamics have changed now. Steven's [Sotloff] family kept to secrecy, and he was executed. Peter's name has been listed.' In the audio recording Peter said his life was in jeopardy if U.S. airstrikes did not stop. 'It was just automatic, kind of toneless, as though he was a robot,' Mrs Kassig said. Peter with his mother as a child. He is the Kassig's only child. The couple said they hope their son will learn of their TV appearance - either directly or indirectly - and 'know we are doing everything we can to secure his release' Mr Kassig and his son - he described his horrified reaction one morning at breakfast when a photo of his son flashed across the TV . 'And I'm sure it's because they were insisting what he could say.' He described that his time was running out,' Paul told TODAY. 'His vitality, his spark was not in his voice.' Peter's captors threatened him in a chilling video showing the beheading of 47-year-old British aid worker Alan Henning on October 3. The couple told how once the video was made public they moved to a hotel to avoid media attention. Mr Kassig described his reaction one morning at breakfast when a photo of his only child flashed across the TV. 'One minute you look at your scrambled eggs and you look up, it's football. Next minute, look at your scrambled eggs, you look up and there's your son,' he said. 'And you sit there and you have to watch. Everybody's jaw on the place drop. And you gotta fake it, too, 'cause you don't want to stand there and look callous. And inside, you just want to scream. 'Hey, that's my kid.' Just ate it, went back upstairs.' Aid worker: Peter Kassig (left), who has been held captive by ISIS for the past year, first went to the Middle East as a U.S. soldier before returning as a medical worker. Right, he is threatened by an ISIS militant . They also speak of the 'demanding' nature of Peter's captors. The Kassigs said ISIS militants have not 'asked' for anything and instead, 'they demand, they simply demand,' Mr Kassig told CBS correspondent Margaret Brennan. Donning a purple jacket and turtleneck top, Mrs Kassig added: 'And their demands have always been ones we cannot accommodate.' Ms Brennan then asked the couple if the demands were 'beyond what is reasonable in terms of money, in terms of power?', to which Mrs Kassig replied: 'In both cases, yes.' Looking down with teary eyes, she continued: 'And we have sent them back messages that we cannot do what you ask. We have tried, but we don't have the power.' In an interview with TODAY they shared portions of a handwritten letter from their son passed on by a former hostage. An inspiration: While in Turkey, Peter (pictured) founded SERA (Special Emergency Response and Assistance), an emergency relief group that serves refugee populations and internally displaced persons . Humanitarian work: It was while working on a project for SERA almost exactly a year ago, on October 1, 2013, that Peter (pictured) was captured by members of ISIS as he headed to Deir Ezzor in eastern Syria . Mr Kassig read from the letter: 'Don't worry, Dad. If I go down, I won't go down thinking anything but what I know to be true, that you and Mom love me more than the moon.' 'He knows that this is bigger than it just being about him,' Mrs Kassig said. 'And we do too.' They explained their son's conversion to Islam saying: 'He was as taken with the religion as he was with the people. 'It was a natural process for him,' said Mr Kassig. Peter, who has been held captive by ISIS for the past year, first went to the Middle East as a U.S. soldier before returning as a medical worker to help victims of war. While in Turkey, he founded SERA (Special Emergency Response and Assistance), a medically-oriented emergency relief group that serves refugee populations and internally displaced persons. It was while working on a project for SERA almost exactly a year ago, on October 1, 2013, that Peter was captured by members of ISIS as he headed to Deir Ezzor in eastern Syria. In the brutal video showing Mr Henning's death earlier this month, Peter was shown kneeling in the desert while a masked militant condemned President Barack Obama for 'aerial bombardments'. The militant added: 'It's only right we continue to strike the necks of your people.' Emotional plea: Mr and Mrs Kassig's latest plea  comes just days after they released an emotional YouTube video (pictured), in which they begged their son's ISIS captors to 'show mercy' and free him . Desperate: On Wednesday, the couple appealed directly to ISIS leader Abu Bakr al Baghdadi on Twitter, begging him to spare their only son's life. Above, Mrs Kassig's tweet, featuring a letter to al Baghdadi . Mr and Mrs Kassig's latest plea to Peter's captors comes just a few days after they appealed directly to ISIS leader Abu Bakr al Baghdadi on Twitter, begging him to spare their only son's life. Mrs Kassig posted a letter on the social networking site, reading: 'I am trying to get in touch with the Islamic State about my son's fate. I am an old woman, and Abdul-Rahman is my only child. 'My husband and I are on our own, with no help from the government. We would like to talk to you. How can we reach you?' Beheading: On October 3, Mr Kassig was threatened with death in a video showing the beheading of 47-year-old British aid worker Alan Henning (pictured). He was seen kneeling in the sand at the end of the footage . The tweet followed an emotional YouTube video, released by the couple on October 4, in which they pleaded to Peter's captors to 'show mercy and use their power to let him go'. Mr Kassig, a school teacher, who was filmed on a sofa alongside his wife, told militants: 'Our family deplores all human suffering and the loss of innocent life, no matter who is responsible. 'We know that the Syrians have suffered. We also believe violence is not the solution to the problems that trouble us all.' Speaking directly to her son, Mrs Kassig, who was donning a headscarf and clasping a photo of the aid worker in her hands, added: 'We are so very proud of you and the work you have done to bring humanitarian aid to the Syrian people. President: Barack Obama (pictured) has condemned the death of Mr Henning and urged that U.S. forces and its allies will bring his killers to justice . 'Our hearts ache for you to be granted your freedom so we can hug you again and then set you free to continue the life you have chosen, the life of service to those in greatest need.' The  beheading of Mr Henning  followed the murders of three other captives in similar circumstances: U.S. journalists James Foley and Steven Sotloff and British aid worker David Haines. U.S. officials have confirmed that Mr Kassig is being held by Islamic State militants, but have declined to give any more details of his capture. The aid worker's family said in a statement earlier this month that they had stayed silent about this news 'at the wish of those who have held their son.' President Barack Obama has strongly condemned the death of Mr Henning and urged that U.S. forces and its allies will bring his killers to justice. 'Mr Henning worked to help improve the lives of the Syrian people and his death is a great loss for them, for his family and the people of the United Kingdom,' the politican said in a statement. 'Standing together with our U.K. friends and allies, we will work to bring the perpetrators of Alan's murder - as well as the murders of Jim Foley, Steven Sotloff and David Haines - to justice.' The President added that the U.S. and other nations will continue to take action to 'degrade and ultimately destroy' the Islamic State group.
Peter Kassig has been threatened with death in a video released by ISIS .
Ed and Paula Kassig hope Peter sees 'we are doing everything we can'
Also speak of their lack of power and captors' 'unreasonable demands'
Mr Kassig was captured by militants while working as aid worker in Syria .
He featured in graphic video showing beheading of hostage Alan Henning .
The parents of American aid worker Peter Kassig who has been captured by ISIS have revealed they have been sent a horrifying audio recording of their son begging for his life. Ed and Paula Kassig, from Indianapolis, said it was the first time they have heard the 26-year-old's voice in over a year and he sounded 'like a robot.' The couple, were ordered by ISIS to keep his capture a secret, but when his picture surfaced on TV days ago, they decided to speak out in hopes their son will hear their words. SCROLL DOWN FOR VIDEOS . Plea: Ed and Paula Kassig, from Indianapolis, the parents of American aid worker Peter Kassig who has been captured by ISIS, have revealed have been sent a horrifying audio recording of their son begging for his life . Ed and Paula Kassig, from Indianapolis, said it was the first time they have heard the 26-year-old's voice in over a year and he sounded 'like a robot' In the audio recording Peter said his life was in jeopardy if U.S. airstrikes did not stop . Sitting in their living room with a school photo of Peter - also known by the Islamic name Abdul-Rahman in the background, Mr Kassig told CBS: 'The dynamics have changed now. Steven's [Sotloff] family kept to secrecy, and he was executed. Peter's name has been listed.' In the audio recording Peter said his life was in jeopardy if U.S. airstrikes did not stop. 'It was just automatic, kind of toneless, as though he was a robot,' Mrs Kassig said. Peter with his mother as a child. He is the Kassig's only child. The couple said they hope their son will learn of their TV appearance - either directly or indirectly - and 'know we are doing everything we can to secure his release' Mr Kassig and his son - he described his horrified reaction one morning at breakfast when a photo of his son flashed across the TV . 'And I'm sure it's because they were insisting what he could say.' He described that his time was running out,' Paul told TODAY. 'His vitality, his spark was not in his voice.' Peter's captors threatened him in a chilling video showing the beheading of 47-year-old British aid worker Alan Henning on October 3. The couple told how once the video was made public they moved to a hotel to avoid media attention. Mr Kassig described his reaction one morning at breakfast when a photo of his only child flashed across the TV. 'One minute you look at your scrambled eggs and you look up, it's football. Next minute, look at your scrambled eggs, you look up and there's your son,' he said. 'And you sit there and you have to watch. Everybody's jaw on the place drop. And you gotta fake it, too, 'cause you don't want to stand there and look callous. And inside, you just want to scream. 'Hey, that's my kid.' Just ate it, went back upstairs.' Aid worker: Peter Kassig (left), who has been held captive by ISIS for the past year, first went to the Middle East as a U.S. soldier before returning as a medical worker. Right, he is threatened by an ISIS militant . They also speak of the 'demanding' nature of Peter's captors. The Kassigs said ISIS militants have not 'asked' for anything and instead, 'they demand, they simply demand,' Mr Kassig told CBS correspondent Margaret Brennan. Donning a purple jacket and turtleneck top, Mrs Kassig added: 'And their demands have always been ones we cannot accommodate.' Ms Brennan then asked the couple if the demands were 'beyond what is reasonable in terms of money, in terms of power?', to which Mrs Kassig replied: 'In both cases, yes.' Looking down with teary eyes, she continued: 'And we have sent them back messages that we cannot do what you ask. We have tried, but we don't have the power.' In an interview with TODAY they shared portions of a handwritten letter from their son passed on by a former hostage. An inspiration: While in Turkey, Peter (pictured) founded SERA (Special Emergency Response and Assistance), an emergency relief group that serves refugee populations and internally displaced persons . Humanitarian work: It was while working on a project for SERA almost exactly a year ago, on October 1, 2013, that Peter (pictured) was captured by members of ISIS as he headed to Deir Ezzor in eastern Syria . Mr Kassig read from the letter: 'Don't worry, Dad. If I go down, I won't go down thinking anything but what I know to be true, that you and Mom love me more than the moon.' 'He knows that this is bigger than it just being about him,' Mrs Kassig said. 'And we do too.' They explained their son's conversion to Islam saying: 'He was as taken with the religion as he was with the people. 'It was a natural process for him,' said Mr Kassig. Peter, who has been held captive by ISIS for the past year, first went to the Middle East as a U.S. soldier before returning as a medical worker to help victims of war. While in Turkey, he founded SERA (Special Emergency Response and Assistance), a medically-oriented emergency relief group that serves refugee populations and internally displaced persons. It was while working on a project for SERA almost exactly a year ago, on October 1, 2013, that Peter was captured by members of ISIS as he headed to Deir Ezzor in eastern Syria. In the brutal video showing Mr Henning's death earlier this month, Peter was shown kneeling in the desert while a masked militant condemned President Barack Obama for 'aerial bombardments'. The militant added: 'It's only right we continue to strike the necks of your people.' Emotional plea: Mr and Mrs Kassig's latest plea  comes just days after they released an emotional YouTube video (pictured), in which they begged their son's ISIS captors to 'show mercy' and free him . Desperate: On Wednesday, the couple appealed directly to ISIS leader Abu Bakr al Baghdadi on Twitter, begging him to spare their only son's life. Above, Mrs Kassig's tweet, featuring a letter to al Baghdadi . Mr and Mrs Kassig's latest plea to Peter's captors comes just a few days after they appealed directly to ISIS leader Abu Bakr al Baghdadi on Twitter, begging him to spare their only son's life. Mrs Kassig posted a letter on the social networking site, reading: 'I am trying to get in touch with the Islamic State about my son's fate. I am an old woman, and Abdul-Rahman is my only child. 'My husband and I are on our own, with no help from the government. We would like to talk to you. How can we reach you?' Beheading: On October 3, Mr Kassig was threatened with death in a video showing the beheading of 47-year-old British aid worker Alan Henning (pictured). He was seen kneeling in the sand at the end of the footage . The tweet followed an emotional YouTube video, released by the couple on October 4, in which they pleaded to Peter's captors to 'show mercy and use their power to let him go'. Mr Kassig, a school teacher, who was filmed on a sofa alongside his wife, told militants: 'Our family deplores all human suffering and the loss of innocent life, no matter who is responsible. 'We know that the Syrians have suffered. We also believe violence is not the solution to the problems that trouble us all.' Speaking directly to her son, Mrs Kassig, who was donning a headscarf and clasping a photo of the aid worker in her hands, added: 'We are so very proud of you and the work you have done to bring humanitarian aid to the Syrian people. President: Barack Obama (pictured) has condemned the death of Mr Henning and urged that U.S. forces and its allies will bring his killers to justice . 'Our hearts ache for you to be granted your freedom so we can hug you again and then set you free to continue the life you have chosen, the life of service to those in greatest need.' The  beheading of Mr Henning  followed the murders of three other captives in similar circumstances: U.S. journalists James Foley and Steven Sotloff and British aid worker David Haines. U.S. officials have confirmed that Mr Kassig is being held by Islamic State militants, but have declined to give any more details of his capture. The aid worker's family said in a statement earlier this month that they had stayed silent about this news 'at the wish of those who have held their son.' President Barack Obama has strongly condemned the death of Mr Henning and urged that U.S. forces and its allies will bring his killers to justice. 'Mr Henning worked to help improve the lives of the Syrian people and his death is a great loss for them, for his family and the people of the United Kingdom,' the politican said in a statement. 'Standing together with our U.K. friends and allies, we will work to bring the perpetrators of Alan's murder - as well as the murders of Jim Foley, Steven Sotloff and David Haines - to justice.' The President added that the U.S. and other nations will continue to take action to 'degrade and ultimately destroy' the Islamic State group.
VIDEOS . Plea: Ed and Paula Kassig, from Peter Kassig who has been captured by ISIS, have indirectly - and 'know we are doing everything we Humanitarian work: It was while working on a October 3, Mr Kassig was threatened with death in a video showing the beheading of 47-year-old British aid worker Alan Henning (pictured). He video, released by the couple on October 4, in