Transcript for Part 4: Ransom Deadline Approaches
Reporter: It was two years ago this summer that Americans were hearing about Isis for the first time, as its leader Abu Bakr Al baghdadi emerged from the shadows, presenting a threat that was now greater than Al Qaeda. But there was no mention in the news of the American hostages, Kayla Mueller, James Foley, Steven sotloff and peter kassig. Their plight remained a closely guarded secret. My name is Carl Mueller, this is my wife Marsha. Reporter: As the 30-day deadline for paying a ransom approached, the muellers recorded this dramatic personal plea, scripted largely by the FBI, and sent to the new Isis leader Al baghdadi. This is a plea for Kayla's life. We are asking for your mercy for Kayla, as we believe you are the only one who can grant us this. These are two people that are in the midst of a horrific experience. I beg you not to harm our daughter. They can't imagine that they would ever be trying to talk on a camera in a respectful fashion to someone who likely going to murder their daughter. Our hands have been tied in trying to raise money, yet we continue to do everything in our power to work toward securing Kayla's freedom. Sir, I am coming to you with a mother's heart, for the love of her daughter. Her mother's got her hair covered. That's critical. It shows respect. Please, show mercy and use your power to free our daughter. That's the way you buy time. That's the way you keep somebody alive one more day. Reporter: It seemed to have worked. The deadline for Kayla's execution, on her birthday, August 14th, passed with no word of her fate, a sigh of relief and a hope that she had seen this part of the video, too. Kayla, we love you. We love who you are, and we admire your compassionate heart and devotion to helping those that suffer. We know god is comforting you and strengthening you. I wish we could see you. Reporter: But it was a very short-lived moment of relief. President Obama is about to speak from Martha's vineyard on the execution of American journalist James Foley by the islamic militants fighting in Iraq and Syria. Reporter: The first of Kayla's fellow American hostages to be murdered. Today the entire word is appalled by the brutal murder of Jim Foley by the terrorist group isil. Reporter: Again the muellers ask to meet with president Obama. We asked to see him and we were told no. Reporter: A few weeks later, another American hostage killed, journalist Steven sotloff, the hostage with whom Kayla had grown close in captivity, with their makeshift trivial pursuit game. Overnight our government determined that, tragically, Stephen was taken from us in a horrific act of violence. Reporter: And now the president agreed to meet with the muellers and the family of the other remaining American hostage, peter kassig. The president was very, I felt, cold. He said, I'm a father, I have two daughters. If that was my daughter being held, I'd do everything I could to get her out. And I'm sure he would have. But we were told many, many times, "We're doing everything we can, everything we can." And they weren't. Reporter: They were not? Well, no, they weren't. Reporter: What the muellers wanted the president to do was allow them to just make an offer of ransom money to Isis for Kayla's life. Carl would say we need to make an offer and then the e-mail would not have anything about an offer in it. Reporter: Because they were all scripted by the FBI? Right. We were like sheep. We were following what the government told us to do. We had no idea. Reporter: In one e-mail, sent under Carl's name, a suggestion of financial hardship. Kayla may not know that I retired this January. Isis was unmoved. Retiring will not help you get your daughter back, so go back to work and earn some money! Reporter: Isis was running out of patience. So no more sentimental sob stories! Reporter: And Carl was increasingly unhappy with what the FBI had written for him to send to Isis. At one point I even said to the team, I said if I got this e-mail back I would be really mad. Reporter: Isis stopped responding. After a while they got the message that this was only stalling. Reporter: Former FBI agent Voss says the FBI should have let the muellers make some kind of a counteroffer. The kidnappers are begging for anything to be thrown onto the table. Anything. At one point in time, they said, "Just give us a benchmark." Reporter: Should there have been a counteroffer? Yes. Keep the conversation going. Keep the hostage alive. Buy more time for a tactical resolution. Reporter: But that did not happen? As far as I know they were never allowed. They were told if they made any sort of an offer they'd be prosecuted, which is unconscionable. Reporter: A white house official, part of its national security staff, delivered that threat of prosecution to the muellers and all the other American hostage families, including the parents of James Foley, who went public after he was killed. We were told very clearly three times that it was illegal for us to try to ransom our son out and that we had the possibility of being prosecuted. And yet meanwhile our son was being tortured and beaten every day.
This transcript has been automatically generated and may not be 100% accurate.