( CNN ) -- Saying she 's an `` old woman '' trying to find out the fate of her only son , the mother of American hostage Abdul-Rahman Kassig has sent a tweet meant for ISIS leader Abu Bakr al Baghdadi . `` I am trying to get in touch with the Islamic State about my son 's fate , '' she says in the tweet , which is a photograph of a letter written to al Baghdadi . `` 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 ? '' Abdul-Rahman Kassig , whose given name is Peter , was detained on October 1 in eastern Syria while doing humanitarian work . ISIS has threatened to kill him next . Since the announcement -- made in an ISIS video showing the apparent beheading of of British aid worker Alan Henning -- Kassig 's has issued repeated pleas asking his captors to show mercy and free him . Over the weekend , they released a YouTube video , imploring his captors to `` use their power to let our son go . '' Wednesday night , Kassig 's parents attended a vigil at Indiana 's Butler University , Kassig 's alma mater . ' I am an idealist ' Kassig , 26 , had already finished a tour in the Middle East as a U.S. Army Ranger stationed in Iraq . But he felt compelled to go back to the region to help Syrians caught in a bloody conflict that has killed roughly 200,000 people . He expressed his fear in captivity in a letter sent to his parents in June . `` I am obviously pretty scared to die , but the hardest part is not knowing , wondering , hoping , and wondering if I should even hope at all , '' Kassig wrote .
In the interview , she says she would like to return to Al Baghdadi . ISIS has threatened to kill Kassig next .