Transcript for New Details on Failed US Commando Rescue Attempt
What a day this has been. We move on to the other big story of this day. The hunt for the brutal killers that took the life of James Foley. The three, mysterious figures believed to be behind the brutal killing. One of the men with what seemed to be a british accent. And now, the urgent worry about another American hostage and the details on the mission that failed. ABC's Brian Ross, with us tonight. Reporter: With growing concern about the fate of a second U.S. Hostage, Steven sotloff, U.S. Officials, today, defended the failed special forces rescue attempt into Syria on the July 4th weekend. The mission was executed flawlessly after significant period of planning and rehearsal. And it turned out the hostages were no longer at that location. Reporter: U.s. Officials say the secret, nighttime mission was launched with several dozen special operations troops, fixed-wing aircraft and helicopters with surveillance drones overhead. Some 15 I.S.I.S. Fighters were believed to be killed. And the United States will not relent on our efforts to bring our citizens home and their captors to justice. Reporter: The U.S. Rescue mission was launched after it became clear that no negotiations were possible with the I.S.I.S. Group, which had commanded a ransom of $130 million for the release of James Foley. FBI didn't take it seriously. We didn't take it seriously. Reporter: People involved in the process say I.S.I.S. Hostages from France and other european countries held by I.S.I.S. Were set free after ransom payments of about $2 million each, paid in cash each, delivered by middlemen in Turkey. Something the U.S. Has refused to consider. Isil has gotten in the millions of dollars from kidnapping of western citizens. And obviously we believe very strongly that we need to cut off their funding. Reporter: As the FBI steps up its investigation, some former hostages identified the man with the knife as one of three british citizens the hostages nicknamed the beatles, who served as jailers, torturers and executioners for the islamic terror group. In a final, chilling e-mail, sent to the parents of James Foley and made public tonight, I.S.I.S. Said, you do not spare our weak, elderly, children or women, so we will not spare yours. That's how Jim Foley's parents learned he would die. What will work to defeat a force as ruthless and implacable as I.S.I.S.? Martha Raddatz is here. What are they talking about today? Well, they're going to continue these air strikes. And they have really been pounding the I.S.I.S. Targets in Iraq. They've pounded about 100 targets since these air strikes began. But they said today at the Pentagon, they are sure I.S.I.S. Will regroup. And chuck Hagel, the secretary of defense, had some really alarming language, calling I.S.I.S., an imminent threat to every interest we have, whether it's in Iraq or anywhere else. What about that phrase, imminent threat? Does that mean a target here in the homeland, in the united States? I don't think he meant that. I think he meant the region. But eventually, they could threaten the homeland. I would not rule out air strikes in Syria. In Syria. Martha Raddatz, Brian Ross, following this story every hour. Thank you so much.
This transcript has been automatically generated and may not be 100% accurate.