 Kayla Mueller Kayla Mueller's parents: Why we feel ISIS wanted to release our daughter Feb. 23, 2015 at 8:29 AM ET 
 
 Kayla Mueller's parents, Carl and Marsha, say that despite fearing for their daughter's safety in captivity at the hands of ISIS, they were holding out hope for a reunion because of frequent contact with her captors. "We always had that little bit of hope that we would always get her home," Marsha Mueller told TODAY's Savannah Guthrie in an exclusive interview. You know, it pretty much made it impossible." Mueller, 26, was confirmed dead on Feb. 10, four days after ISIS claimed she had been killed in an airstrike in Syria. The Muellers said communication with their daughter's captors fell apart once the White House agreed last year to trade American soldier Bowe Bergdahl, held for five years in Taliban captivity, in exchange for five Taliban detainees being kept in Guantanamo Bay. Kayla Mueller Read Kayla Mueller's last letter to her family: 'My heart longs to be with you' Feb. 23, 2015 at 8:20 AM ET 
 
 The family of Kayla Mueller, the U.S. aid worked killed while in ISIS custody, spoke to Savannah Guthrie in their first interview since Kayla's death. "That made the whole situation worse because that's when the demands got greater," he said. "They got larger. They realized that they had something." "I actually asked the president that question when we were in the White House," Carl Mueller said without elaborating. "Yeah, that was pretty hard to take.” 
 
 Matt Hinshaw / EPA 
 
 He also expressed frustration with a U.S. government policy that forbids paying ransoms for the lives of American citizens, noting other Western countries have paid millions to secure the release of their nationals. “We understand the policy about not paying ransom, but on the other hand, any parents out there would understand that you would want anything and everything done to bring your child home,” Carl Mueller said. The Pentagon said it didn't know how she was killed. All my everything, 
 
 Kayla 
 
 Courtesy of the Mueller Family 
 
 This paper was found in Kayla's room by her parents after her disappearance. Meanwhile, Kayla Mueller's mother said in the TV interview that she was still "in denial" about her daughter's death. Courtesy of the Mueller family 
 
 Courtesy of the Mueller family 
 
 To learn more about the family's effort to honor Kayla's life, visit their non-profit foundation, Kayla's Hands.
– Kayla Mueller's family previously released what was billed as her last letter to them, but now they've released another, and this one is reportedly the final communication they received from her before she was killed while an ISIS captive. Today has it in full. "Once again you are being contacted by prisoners who have been released," it opens. "As I said in my last letter (that I pray you received from the three women) I am OK, healthy, remaining strong and being treated kindly. Do not worry ... I love you all." She goes on to ask them to pray, then shares part of a song she wrote for "little Lex" with the line, "Oh my Grace. I close my eyes, you bring me home." "I look towards the day when I can sing to her the rest. I do not know what you have told her, but if it's appropriate, tell her Auntie Kayla sends her big hugs and kisses," she writes. "Tell her I am very sad that I am far and that we cannot Skype like before, but when I come home we can play, make music together and have so much fun ... She's my little Grace and I love her so much." Once again, she signs the letter, "All my everything, Kayla." Click for the full letter, as well as other writings her family has shared. Mueller's dad, Carl, says in a Today interview that the US put "policy" ahead of a citizen's life. In the same interview, which aired today, Mueller's brother says her situation got worse after the US swapped five Taliban commanders for Army Sgt. Bowe Bergdahl in May, the AP reports. "That's when the demands got greater," he says. "[ISIS] realized that they had something."