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 Friends and family of slain ISIS hostage Kayla Mueller said they hoped her death would achieve what she'd worked for before she was kidnapped: raising the awareness of Syrian refugees. 
 
 "The things that were important to Kayla are finally getting the attention they deserve," aunt Lori Lyon said in a tearful news conference in her hometown of Prescott, Arizona, Tuesday — hours after the family confirmed that Mueller had died while in ISIS' hands. 
 
 The Rev. Kathleen Day, who runs the United Christian Ministry at Northern Arizona University, where Mueller was a student, recalled following her blog posts from Syria. "I hope you can tell the entire world here what I've said here, and what I've seen," Mueller wrote, according to Day. The pastor also recalled Mueller's recollection of refugees' frequent response when they learned she was American: "Where is the world?" 
 
 "We're right here, Syria," Day said. "We've seen your suffering reflected in Kayla's eyes." 
 
 Eryn Street, a close friend of Mueller's, recalled her seemingly limitless empathy. "She had an amazing ability to share in someone else's suffering and add a little happiness to it," Street said. 
 
 She added: "I'm not yet sure how to live in a world without Kayla, but I do know we're living in a better world because of her." 
 
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 In an interview with BuzzFeed News on Tuesday, President Obama called Mueller "an outstanding young woman and a great spirit — and I think that spirit will live on." 
 
 He added, "I think the more people learn about her, the more they appreciate what she stood for and how it stands in contrast with the barbaric organization that held her captive ... but I don't think it's accurate ... to say that the United States government hasn't done everything we could." 
 
 The family of Abdul-Rahman Kassig, another American aid worker who was captured by ISIS and who was murdered by the group, offered its condolences Tuesday. 
 
 We mourn with the Muellers over the death of their daughter, Kayla Mueller. She lived a life of service. She will be remembered! — Kassig Family (@kassigfamily) February 11, 2015 
 
 Mueller, 26, was confirmed dead Tuesday morning, four days after ISIS claimed she'd been killed by a coalition airstrike in Syria. 
 
 A senior U.S. official said the evidence consisted of a photograph emailed to the family and "appears to show her dead with trauma injuries." But the official said the injuries were not consistent with injuries suffered by victims of an airstrike. 
 
 Jen Psaki, a U.S. State Department spokeswoman, said the government were not able to confirm a cause of death. "The U.S. military has indicated that there was no evidence of civilians in the target area prior to any recent coalition airstrikes," Psaki said. 
 
 Kayla Jean Mueller in a photo released by her family. Family Photo 
 
 Pentagon spokesman Rear Admiral John Kirby on Tuesday also dismissed ISIS' assertion that the Jordanian air strike was responsible for Mueller's death. 
 
 "Let's not forget in whose hands this woman died. And let's not forget who's ultimately responsible for it: ISIL," Kirby said, using an alternate acronym for the Islamic State in Iraq and al-Sham. 
 
 Mueller traveled to the Turkish-Syrian border to work with refugees in December 2012, and was taken captive in Aleppo, Syria on Aug. 4, 2013, while leaving a Doctors Without Borders hospital. Her family asked the media to keep her name out of the press out of fears it would endanger her life. 
 
 Mueller was among the U.S. hostages Army Delta Force commandos unsuccessfully tried to rescue in an operation in Raqqa last July. And Congressman Paul Gosar, a Republican whose district encompasses Mueller's hometown, told the Arizona Republic this week that there were other plans to rescue Mueller that either failed or were shot down by her family as too risky. ||||| American special operations forces and FBI agents on the ground in Syria are actively searching sites where they believe Western hostages, including Americans executed by ISIS, may have been buried, counterterrorism officials told ABC News. 
 
 Interested in Syria? Add Syria as an interest to stay up to date on the latest Syria news, video, and analysis from ABC News. Add Interest 
 
 Three officials briefed on the ground searches by U.S. commandos -- the first real effort to recover the remains of two American journalists and two American humanitarian aid workers killed from 2014 to 2015 -- said they were undertaken on the basis of new intelligence from two ISIS members from London captured last month by Syrian Kurds. 
 
 “Intel people are digging hard and directing ground guys to locations,” a counterterrorism official who is not authorized to speak publicly told ABC News. 
 
 Two other counterterrorism officials confirmed to ABC News that ground searches have begun and suggested the efforts are limited so far but could be expanded. The remains are believed to be spread out over several sites. 
 
 Syrian Democratic Forces/Handout via Reuters 
 
 Alexanda Kotey and El Shafee Elsheikh are two of the most important ISIS figures ever captured on the battlefield. U.S. commanders at Joint Special Operations Command and CIA have had a policy of carrying out targeted killings with armed drones of the terrorist group's senior leadership rather than more risky attempts to capture them. 
 
 The two ISIS fighters taken prisoner last month were half of a quartet of British guards — dubbed the "Beatles" by the hostages — who tortured and beheaded their captives. Their leader, Mohammed Emwazi, was called "Jihadi John" and died in a CIA airstrike in Raqqa, Syria, in November 2015. Another member, Aine Davis, was captured in Turkey last year. 
 
 The two men are being interrogated by U.S. officials and are providing information about burial sites of American hostages they tormented and executed while running a kidnap and ransom operation for ISIS, which began in 2013. Ransom demands were halted after a July 4, 2014 failed Delta Force rescue raid and the subsequent U.S.-led coalition air campaign against ISIS. 
 
 AP, FILE 
 
 The U.S. Hostage Recovery Fusion Cell has contacted families of the hostages who died -- some of whom were shown having their heads cut off by Jihadi John on video -- many of whom welcomed the capture of the pair and U.S. efforts to find the remains of their loved ones. 
 
 Diane Foley, mother of journalist James Foley, the first to die on video in August 2014, told ABC News, that knowing that U.S. forces are searching for burial sites of her son and his fellow captives is emotionally difficult but gratifying. 
 
 "I am grateful for all these efforts but bringing these two jihadists to justice gives us more hope and solace than the return of Jim's remains," she said. 
 
 Foley's execution was followed by the killings on video of fellow American hostages Steven Sotloff, a journalist, and Abdul-Rahman (Peter) Kassig, a humanitarian medic and former Army Ranger. Five more men — two from Britain, two from Japan and one from Jordan — also died in horrific videos released over several weeks by ISIS into early 2015. 
 
 Kayla Mueller was the only westerner whose death did not play out in a Jihadi John video. ISIS announced the death of the humanitarian aid worker from Prescott, Ariz. in a Feb. 6, 2015 tweet, claiming a Jordanian airstrike killed her in Syria. The captors sent her parents three photos of her lifeless face when they asked for proof. 
 
 "I don't know what happened to Kayla. I don't where Kayla is. I need her home," said her mother, Marsha, on Friday. "She belongs here." 
 
 Matt Hinshaw/The Daily Courier via AP, FILE 
 
 Kayla's father, Carl Mueller, said he appreciates that any effort to recover the remains of his only daughter, whose death is still a mystery. The Muellers recently pressed U.S. hostage recovery officials in a Washington briefing to reveal how their daughter died and were told specific details have eluded investigators. 
 
 "Unlike the other families, we don't have the gruesome execution video,” Carl Mueller told ABC News. “We need to know she's gone.” 
 
 Beyond the effort to examine sites in Syria, the Muellers want any information about Kayla's last days, when according to fellow captives who later escaped she was forced to be the sex slave of Abu Bakr al-Baghdadi, the leader of ISIS. Sources have told ABC News that al-Baghdadi is believed to have been most likely killed in a U.S. airstrike in July, though his death was never confirmed. 
 
 "I would like anyone who has information about Kayla to share that with us," her mother said. 
 
 That includes Kotey and Elsheikh, who may know how she died and where she is buried. 
 
 According to J.M. Berger, author of “ISIS: The State of Terror,” Kotey and Elsheikh are the most important ISIS figures captured in several years. 
 
 "This is a really big development," Berger said. "ISIS has provided an incredible documentation of its atrocities and we haven’t seen anyone held to account for that. It would be hard to see how these guys could get off. People need to see justice being done." ||||| Too Slow 
 
 The U.S. did not think British intelligence was good enough to act on and waited a month to launch a mission to rescue ISIS's hostages. By then it was too late. 
 
 The U.S. government obtained intelligence on the possible location of American captives held by ISIS in Syria last year, but Obama administration officials waited nearly a month to launch a rescue mission because of concerns that the intelligence wasn’t conclusive and some of it had come from a foreign service, U.S. and British officials told The Daily Beast. 
 
 British officials, as well as private security contractors, said they were frustrated by Washington’s hesitance to give the go-ahead for a rescue attempt, which eventually was carried out on July 4, 2014, by which time the hostages had been moved. The following month, ISIS began beheading its American and British prisoners in a series of grisly Internet videos. 
 
 Toward the end of May, the British government had identified two or three locations in and around the Syrian city of Raqqa, the de facto capital of the so-called Islamic State, where the militants had moved hostages during the previous weeks and months. But the British were not absolutely sure in which location the Westerners were held. The captives included American journalists James Foley and Steven Sotloff, as well aid worker Kayla Mueller. The information—based on debriefings of European captives who had been released, satellite and drone surveillance, and electronic eavesdropping—was not definitive in May. 
 
 Then, in early June, London had a “positive identification and that information was shared with Washington,” said a British source. The delay of nearly a month before the rescue bid was mounted remains a source of bewilderment for British officials. 
 
 But a U.S. official said that inside the White House, Obama’s senior national-security advisers were not willing to base a raid on intelligence developed by a foreign service. “The issue was that they didn’t trust it, and they wanted to develop and mature the intelligence, because it wasn’t our own,” said the U.S. official, who asked to remain anonymous when discussing sensitive hostage-rescue efforts. 
 
 “They got the information. They just didn’t trust it. And they did sit on it, there’s no doubt about that,” the official said. 
 
 Bernadette Meehan, National Security Council spokesperson, told The Daily Beast: “U.S. forces conducted this [rescue] operation as soon as the president and his national-security team were confident the mission could be carried out successfully and consistent with our policies for undertaking such operations.” 
 
 But Diane Foley, the mother of James Foley, who was the first American to be shown murdered on camera, also raised questions about the timing of the rescue effort, telling The Daily Beast that French officials had developed information about the hostages’ location as early as March, but that the U.S. government didn’t act on it. 
 
 “That was part of our frustration,” she said. “The State Department said they were connecting with the French and everybody at the highest levels.” And yet, there was no movement on the U.S. side. “Very specific information was available as early as mid-March. And that’s what’s been so tough for us as families, because apparently they were held in the same place all those months,” Foley said. 
 
 Last August, after the administration disclosed the failed raid, National Security Adviser Ben Rhodes pushed back against the suggestion that the United States hadn’t done enough to win the release of the American captives. 
 
 “I can assure you that we have done everything that we can possibly do to try to bring home our hostages,” Rhodes said during a press briefing on Martha’s Vineyard. “It’s an incredibly difficult circumstance in a place like Syria, again, where you have such a violent conflict raging. But we’ve used all of our military, intelligence, diplomatic resources that we can bring to bear to try to pull a thread to find out where our hostages are; to try to rescue them when we saw an opportunity; to try to work with any country that might have any means of locating them.” 
 
 U.S. intelligence agencies had also debriefed European hostages who were released after their governments made ransom payments. The Washington Post reported last August that the president had authorized a rescue attempt “earlier this summer,” citing a senior administration official. 
 
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 “We had a combination of... intelligence that was sufficient to enable us to act on it,” the official told the Post, and the military moved “very aggressively, very quickly to try and recover our citizens.” 
 
 Rescue missions are inherently dangerous, and recent attempts have ended in the death of the hostages. But family members of the Americans held by ISIS, including the parents of Foley and Sotloff, as well as Foley’s brother, have said the U.S. government did not do enough to rescue their loved ones. 
 
 Responding to the general criticism of the United States being slow to act, President Obama told BuzzFeed this week, “I don’t think it’s accurate then to say that the United States government hasn’t done everything that we could. We devoted enormous resources—and always devote enormous resources—to freeing captives or hostages anywhere in the world, and I deployed an entire operation at significant risk to rescue not only [Mueller], but the other individuals that had been held, and probably missed them by a day or two, precisely because we had that commitment.” 
 
 The question of U.S. rescue efforts has taken center stage again with the death of Mueller, a 26-year-old aid worker who was taken captive in Syria in 2013. U.S. officials and Mueller’s family confirmed this week that she was killed while held hostage by ISIS, although the cause of her death has not been determined. 
 
 Questions are now being asked of Mueller’s then-boyfriend, who was with her when they and two others were snatched by ISIS after visiting a Doctors Without Borders hospital near Aleppo on Aug. 4, 2013. He is a Damascus-born freelance photographer who had also undertaken some projects for the Danish Refugee Council and worked for a time as a staff reporter at Reuters. The pair met in Cairo, according to a former colleague who worked with the man. 
 
 After the pair were detained, ISIS let Mueller’s boyfriend go—a move that later prompted some speculation that he might have been involved in the abduction. But those fears were dispelled when, at great risk to himself, he went to Raqqa to try to negotiate her freedom. He claimed to be her husband, but Mueller reportedly told her captives that she wasn’t married. It’s not clear whether she was aware that her boyfriend had returned for her. But he was seized and held for two months, from December 2013 to January 2014, before being set free again. 
 
 “He was besotted with [Kayla],” said the man’s former colleague. “There was talk before her capture of an engagement.” In an email to The Daily Beast, the photographer declined to be interviewed, writing, “let me take my time to understand what happened and to bring myself all together.” He has also declined interview requests from private security contractors working on hostage cases. 
 
 Writing under the pseudonym Omar Alkhani on Facebook, the man has posted romantic missives to Mueller. In a post apparently written after learning of confirmation of Mueller’s death, he bid her farewell. “Thank you for coming into my life and giving me joy, thank you for loving me and receiving my love in return,” he wrote in one post. “You were everything I wanted. You were so beautiful and charming, and you supported me in everything I did, even if it was extremely stupid.” 
 
 “Alkhani” generally avoided writing about her after her capture, but in September 2013 posted, “My heart is in your detention cell/it lives your pain all day/you are not alone/you are not alone.” 
 
 On Wednesday, reports surfaced that Mueller may have been given as a bride to an ISIS fighter. But British sources questioned the claim, saying it was the first they had heard of it and it didn’t crop up in any “chatter they were monitoring” or in communications between London and Washington. “I find the report dubious: She had potential monetary value for them as far as they were concerned,” says a British source. 
 
 ISIS claims that Mueller was killed last week in a Jordanian airstrike conducted in revenge for the group burning alive a Jordanian pilot. The Jordanians dismissed the allegation as ISIS “spin,” and U.S. officials have said they have no information on how Mueller died.
– President Obama says his reaction to the death of ISIS hostage Kayla Mueller is "heartbreak"—but he thinks her "great spirit" will live on. "The more people learn about her, the more they appreciate what she stood for—and how it stands in contrast with the barbaric organization that held her captive," he tells BuzzFeed in an interview yesterday. He stresses the government did all it could to free her, including deploying an entire operation "at significant risk" to free her and other US hostages. The government did, however, stick to its policy of not paying ransoms to organizations like ISIS; ABC News reports ISIS demanded $6.6 million for her release, and had set an August 2014 deadline for payment. More emerging details: Although the government says it has been unable to confirm the cause of Mueller's death, per the New York Times, ISIS sent Mueller's family three photos of her body, according to two people briefed on the family's correspondence with ISIS. Two photos reportedly showed Mueller in a black Muslim hijab that partly covered her face; the third showed her in a traditional white burial shroud. And while the Times sources said they saw bruises on Mueller's face in the photos, there was no evidence of "puffiness or other concussive effects associated with a bomb blast," though they acknowledge she could have been located in a nearby building or injured by flying debris. The rescue operation referenced by Obama took place July 4 in a predawn raid on a Raqqa prison by Delta Force commandos, the Los Angeles Times reports. But the two dozen soldiers were too late: The hostages—who also included James Foley and Steven Sotloff—had apparently been moved a day or two before. "We never stopped trying to get her," a defense official not authorized to speak publicly tells the Times. "We never lost that focus." Officials yesterday told ABC News that Mueller may have been "given over" to an ISIS commander, and that forced marriage could have even been involved. "ISIS didn't see her as a hostage or a bargaining chip," said one. Devastated friends and relatives in Mueller's hometown of Prescott, Ariz., say they hope her death will raise awareness of the plight of the Syrian refugees she worked with, NBC reports. "The things that were important to Kayla are finally getting the attention they deserve," an aunt said. "The world grieves with us."