Editor's Note: On Friday, Feb. 6. 2015, ISIS said the hostage was killed by a Jordanian airstrike. 
 
 With ISIS’s brutal murder of Peter Kassig, a 26-year-old American aid worker who dedicated his life to the plight of Syrian refugees, the militant group has one more U.S. citizen remaining in its clutches, according to current and former U.S. officials, as well as individuals involved in efforts to free the Americans. 
 
 The hostage is the only American woman held by the militant group. She is the same age as Kassig, and, like him, was kidnapped while trying to help people whose lives have been upended by the long Syrian civil war. She was particularly moved to help children who have been orphaned and separated from their families. The woman was taken in August 2013, along with a group of other aid workers who have reportedly been released. 
 
 U.S. officials and the woman’s family have requested that her name not be made public, fearing that further attention will put her in greater jeopardy. No news organization has published her name. But the general circumstances of her capture and captivity have been known and widely reported for more than a year now. 
 
 ISIS’s intentions for its remaining American prisoner are unclear. But current and former U.S. officials told The Daily Beast that it was notable she doesn’t appear at the end of a video, released Sunday, that shows the aftermath of Kassig’s beheading. That breaks with ISIS’s pattern of showing the next hostage it intends to kill. 
 
 ISIS has killed Muslim women, as well as children. But it has never murdered a female Western hostage on camera. Doing so would mark a radical departure even for a group that has relied on bloody propaganda to lure foreign fighters to its ranks. 
 
 A former U.S. counterterrorism official said that before ISIS decides what to do with its remaining American hostage, it will consider carefully the public reaction it could spark. “Before they’re doing anything, they want to have a really good feel for how it will play,” the former official said. 
 
 ISIS has reportedly demanded more than $6 million for the remaining American hostage’s freedom, a figure in keeping with the impossibly high ransoms it has placed on other U.S. citizens it has held. The Obama administration has a firm policy of not paying ransom for hostages and has even advised the families of Americans held in Syria that they could be criminally prosecuted if they paid for their loved ones’ releases. (ISIS has freed European citizens, however, from countries where ransoms aren’t illegal.) 
 
 The fact that ISIS requests any ransom for its American prisoners and makes it too high for most people to pay indicates that the group isn’t really serious about freeing the Americans, according to current and former U.S. officials and hostage-negotiation experts. Instead, the hostages are being used as props in ISIS’s global propaganda campaign, which is largely aimed at recruiting new followers. Viewed through that lens, ISIS’s American and British captives (the U.K. likewise has an official ban on ransoms) have been more useful to the group for its videos than in raising money, even though ransoms are an important source of ISIS’s income. 
 
 The latest ISIS video, showing Kassig’s death, had been expected ever since he was first shown on camera in early October, in another beheading video, and identified as the militant group’s next victim. But this new film differs in key respects from its predecessors, and it may offer new insights into ISIS’s propaganda strategy—and its weaknesses. 
 
 The latest video is uncharacteristically long, clocking in at more than 16 minutes, as opposed to the earlier two- to three-minute films showing hostages being murdered. The new video is filled with breathless celebration of the rise of the so-called Islamic State and an exhortation to its followers to join in armed struggle against the “crusader” forces of the United States and the United Kingdom. Indeed, it seems rather desperate in its chest-thumping. It’s also remarkably more brutal—though not to American hostages. A parade of knife-wielding ISIS fighters behead 18 captives, described as Syrian military officers and pilots, in a ghoulish display filled with slow-motion effects and ominous music. It’s by far the most grisly depiction of beheadings ever shown by ISIS. 
 
 Kassig is shown only near the end of the video, already beheaded. Unlike other hostages who have read (presumably coerced) statements denouncing the U.S.-led airstrikes, Kassig is never shown speaking. His killer alludes to the fact that he had “little to say” and that other American captives killed before him had already spoken out against the Obama administration. Several current and former U.S. officials speculated that Kassig, who converted to Islam while in captivity and adopted the name Abdul Rahman, might have defied his captors by refusing to read their script or even have insisted on reciting passages from the Quran. “I suspect that Pete knew this was coming and that he refused to talk,” said one individual who has been involved with efforts to free American hostages. 
 
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 Kassig’s parents had made his conversion to Islam, which they described as genuine and profound, a central pillar of their highly public efforts to free him. The Kassigs, of Indiana, had given television interviews about their son, made YouTube videos pleading with ISIS for his release, and held prayer vigils with members of the American Muslim community. At every turn, they described their son as a faithful follower who had dedicated his life to easing the suffering of innocents. 
 
 In a statement Sunday, Kassig’s parents said their son was “fed by a strong desire to use his life to save the lives of others” and that he “was drawn to the camps that are filled with displaced families and to understaffed hospitals inside Syria. We know he found his home amongst the Syrian people, and he hurt when they were hurting.” 
 
 President Obama, also in a statement, called Kassig by his chosen Muslim name and contrasted his charity and self-sacrifice with the “darkness” of ISIS. Secretary of State John Kerry called Kassig “a young American who personified the values of altruism and compassion which are the very essence of his adopted religion of Islam.” 
 
 ISIS’s long-winded video recites chapter and verse the historic roots of the group, from its early days in Iraq fighting U.S. forces in 2004, and seeks to position the rise of ISIS as an inevitable development in a grand battle against the “crusaders.” The video also argues that ISIS is collecting followers across the Middle East, even as far east as China. 
 
 ISIS has a reason to buck up its forces and make itself seem invincible: U.S. airstrikes against the group are starting to yield some results. On Saturday, Iraqi ground forces, supported by American aircraft, took back an important oil refinery in Baiji, about 130 miles north of Baghdad, that ISIS had seized. (Illicit oil revenue has been a major source of the group’s funding.) And the U.S. has been closing in on ISIS’s leader, Abu Bakr al-Baghdadi, though efforts to kill him and his followers have been frustrated by ISIS’s use of encryption to shield its communications from American surveillance efforts. 
 
 Still, the video is a reminder of how feckless U.S. efforts to free American hostages have become. Insiders have said the process has been marred by bureaucratic turf wars and a refusal by the United States to negotiate with ISIS, which has freed European hostages in exchange for ransom. 
 
 The State Department and the White House have been opposed to paying ransoms, but the FBI and the Justice Department have taken a more nuanced position, according to people involved in the efforts. In particular, the FBI told the parents of James Foley, the first American whom ISIS killed on camera, that they could “walk us right up to that point” of paying a ransom but not be directly involved in exchanging funds, Diane Foley, James’s mother, told The Daily Beast last month. 
 
 The FBI has facilitated the payment of a ransom for American hostages before, most notably in 2002, for the release of two Christian missionaries, Martin and Gracia Burnham, who were held by an al Qaeda affiliate in the Philippines. A former U.S. official said the FBI took steps to obscure its role and that the terrorists never knew the U.S. government was involved in the ransom effort. 
 
 More recently, a ransom allegedly was paid to free American journalist Peter Theo Curtis in August from al-Nusra Front, al Qaeda’s branch in Syria, according to two sources with direct knowledge of Curtis’s case. Suspicion has focused on the government of Qatar, which has strong ties to Nusra, as the source of the money. 
 
 A spokesperson for the State Department has denied that the United States paid a ransom, and administration officials told the Qataris they shouldn’t pay one, either. FBI spokesman Paul Bresson said that the bureau fully complies with U.S. policy as it relates to ransom payments. According to individuals familiar with the matter, Nusra may have hoped that by negotiating for Curtis’s release, it would demonstrate to the United States that it wasn’t as extreme as ISIS and could engage in a reasonable dialogue. 
 
 Those hopes might be dashed, however, by U.S. airstrikes in Syria, which have hit Nusra positions, provoking the group’s wrath. Prior to the bombing campaign, which began in September, U.S. intelligence officials warned not to hit the Nusra group, which occasionally has fought alongside U.S.-backed rebels in Syria. Now Nusra is forging an alliance with ISIS, an outcome that had once been considered unthinkable because of a deep schism between ISIS and al Qaeda over the future of the Islamist movement. 
 
 How that might effect the Westerners still held in Syria is unknown. The-26 year-old aid worker being held by ISIS isn’t the only one. Freelance journalist Austin Tice was abducted in Syria more than two years ago. The Obama administration has claimed that Tice was held by the Syrian government. But this claim has never been verified and who holds him now is unclear. ||||| Media playback is unsupported on your device Media caption "The 26-year-old American was captured last year" 
 
 A video posted online claims to show that Islamic State militants have killed the captured US aid worker Abdul-Rahman Kassig. 
 
 The video shows a masked man standing over a severed head which he says is that of Mr Kassig. 
 
 The US says it is working to determine the authenticity of the video, which also shows a mass beheading of 18 Syrian troops. 
 
 Mr Kassig, also known as Peter, was captured last year. 
 
 His family, who live in the US state of Indiana, said they were awaiting confirmation of the reports about their "treasured son". 
 
 "We prefer our son is written about and remembered for his important work and the love he shared with friends and family, not in the manner the hostage takers would use to manipulate Americans and further their cause," the family said in a statement. 
 
 Analysis: Frank Gardner, BBC security correspondent 
 
 Media playback is unsupported on your device Media caption The BBC's security correspondent Frank Gardner: "This is an act of desperation" 
 
 This is perhaps the most elaborate and graphic of all the murder videos posted online by IS. Much of it is taken up with a recent history lesson on Iraq and Syria as seen through the eyes of the jihadists. But the latter part shows the beheading of 18 Syrian prisoners in revolting, lingering detail. 
 
 Unlike earlier videos, this one revels in gore. Amongst the boiler-suited captives murdered in cold blood is a man IS says is the former US soldier Peter Kassig, who converted to Islam and changed his name to Abdul-Rahman. 
 
 Neither his conversion, nor the fact that he was helping refugees when he was captured a year ago, appear to have saved him. 
 
 Mr Kassig's murder is a sign of frustration that IS militants are unable to hit back at the coalition air strikes that have driven them off key sites like the Mosul and Haditha dams, and prevented them from seizing the town of Kobane. 
 
 An idealist 'simply trying to help people' 
 
 Abdul-Rahman Kassig in his own words 
 
 Unlike similar videos released in the past, the latest shows the faces of many of the jihadis. It also at one point gives a specific location - near Dabiq in Aleppo province, with an identifiable village in the background. 
 
 The latest video did not show the person identified as Mr Kassig being beheaded. Also unlike previous videos, it did not show other Western captives or directly threaten to behead anyone else. 
 
 The US National Security Council said it was investigating the video, and would be "appalled by the brutal murder" if it was confirmed. 
 
 IS has previously murdered four Western hostages - British men Alan Henning and David Haines, and US journalists James Foley and Steven Sotloff. 
 
 Those killings were carried out by a man believed to be British. That man bears a resemblance to one of the masked militants pictured in the video purporting to show Mr Kassig. 
 
 Image copyright EPA Image caption Parents Ed and Paula Kassig have said they are awaiting confirmation of the reports 
 
 British Prime Minister David Cameron said he was "horrified by the cold-blooded murder" and that Islamic State had "again shown their depravity". 
 
 Emotional letter 
 
 Image copyright Handout Image caption A photograph of Abdul-Rahman with his father, Ed, fishing on the Ohio River in Indiana in 2011 
 
 Mr Kassig's parents last month released extracts of a letter written by their son, in which he said the "stress and fear" of captivity were "incredible". 
 
 "They tell us you have abandoned us and/or don't care but of course we know you are doing everything you can and more. 
 
 "Don't worry Dad, if I do go down, I won't go thinking anything but what I know to be true. That you and mom love me more than the moon and the stars." 
 
 Media playback is unsupported on your device Media caption Former hostage Nicholas Henin spoke to the BBC about Mr Kassig in October 
 
 Mr Kassig was a former US Army Ranger who served in Iraq. 
 
 He later trained as an emergency medical technician and founded the Special Emergency Response and Assistance (Sera) organisation, helping to supply camps on both sides of the Syrian border. 
 
 He was undertaking a project for Sera when he was captured in October 2013 while travelling to eastern Syria. 
 
 The exiled leader of Syria's opposition National Coalition, Hadi al-Bahra, said in a statement Mr Kassig would be remembered as a hero. 
 
 "Kassig paid the ultimate sacrifice trying to relieve the suffering of his fellow human beings far away from home. The thugs of Isis will pay the price for their evil crimes," he said. ||||| Story highlights Kassig is the fifth Western hostage ISIS apparently beheaded 
 
 He converted to Islam during his captivity and also went by the name Adbul Rahman Kassig 
 
 He was a former U.S. soldier who became a medical worker 
 
 He wanted to help the victims of war and was captured in Syria a year ago 
 
 American aid worker and former soldier Peter Kassig was beheaded by ISIS terrorists, the White House confirmed Sunday, hours after a video claiming to show the victim surfaced online. 
 
 ISIS held Kassig as a hostage and in previous communications had threatened his life. 
 
 The video shows the aftermath of a beheading in which the victim is not clearly recognizable. 
 
 President Barack Obama confirmed the 26-year-old's beheading, saying Kassig "was taken from us in an act of pure evil by a terrorist group that the world rightly associates with inhumanity." 
 
 Kassig, who converted to Islam in captivity, also went by the name Abdul-Rahman Kassig. 
 
 He first traveled to the Middle East as a U.S. soldier and returned as a medical worker, feeling compelled to help victims of war. 
 
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 He did aid work in Syria, where he was captured. He was held hostage for over a year. 
 
 "We are heartbroken to learn that our son, Abdul-Rahman Peter Kassig, has lost his life as a result of his love for the Syrian people and his desire to ease their suffering," Kassig's parents, Ed and Paula, said in a statement. 
 
 The parents released a previously unpublished audio recording of their son, recorded by a journalist before Kassig was taken captive. 
 
 "You know we would have a chance here to make up for a lot wrong that we did in this part of the world if we stepped in, in the right way," Peter Kassig says in the recording. "If we just as a country did what other people helped me to do in that hospital. How much did I impact the political situation inside Syria? None. How much did I impact the political situation back home? None. But what I did do is that over period of time in that hospital I was able to share a little bit of hope and comfort with some people." 
 
 The Kassig family expressed heartbreak over the beheadings of the other Westerners who came before their son, and asked for prayers for the safe return of other captives. 
 
 "While ISIL revels in the slaughter of innocents, including Muslims, and is bent only on sowing death and destruction, Abdul-Rahman was a humanitarian who worked to save the lives of Syrians injured and dispossessed by the Syrian conflict," Obama said. 
 
 ISIL is another term for the group ISIS, the Islamic State in Iraq and Syria, which calls itself simply the Islamic State. 
 
 The video 
 
 A familiar figure appeared in Sunday's beheading video, dressed in all black and speaking with what sounds like an English accent. 
 
 A man fitting the same description appeared in previous videos of the apparent beheadings of other Westerners. 
 
 But this recording is different from previously released ones. It is longer, almost 16 minutes, and does not include a statement by the victim, as previous ones had. 
 
 And it is utterly brutal, showing in graphic detail the beheadings of other men, whom militants claim are pilots for the Syrian government. 
 
 The narration spends much time on ISIS' history and the figure taunts Obama, saying he will have to return troops to Iraq in greater numbers than before. 
 
 And for the first time in such a video, the speaker names the place where he is standing with the victim -- in the town of Dabiq in Aleppo province, Syria. 
 
 The fifth Westerner 
 
 Kassig is the fifth Westerner whom ISIS claims to have beheaded via video messages. 
 
 The first was U.S. journalist James Foley. A video of his killing was posted online in mid-August, just over a week after Obama approved "targeted airstrikes" against ISIS. 
 
 In early September, ISIS released a video showing the beheading of U.S. journalist Steven Sotloff. Sotloff's apparent killer spoke in what sounded like the same British accent as the man who purportedly killed Foley. 
 
 Less than two weeks later, ISIS announced in a video the apparent killing of British aid worker David Haines. 
 
 And on October 3, ISIS released a video showing the apparent beheading of hostage Alan Henning. 
 
 Secretary of State John Kerry praised Kassig's compassion and reiterated the goal of defeating ISIS. 
 
 "This was a young man who traveled to one of the world's most dangerous places to care for the innocent victims of a bloody conflict, and fearlessly dedicated himself to helping those in need," Kerry said. "There can be no greater contrast than that between Abdul-Rahman's generosity of spirit and the pernicious evil of ISIL." 
 
 Plea for mercy 
 
 Kassig's life was threatened on the video that showed Henning's killing. 
 
 A week after its release, Kassig's family released a YouTube video of their own, asking his captors to show mercy and free him. 
 
 Kassig's mother, Paula, addressed her son in the video. "We are so very proud of you and the work you have done to bring humanitarian aid to the Syrian people," she said. 
 
 The couple noted they were releasing the video on the day of Islam's Eid al-Adha, or the Festival of Sacrifice, when Muslims slaughter lambs, goats, sheep and cattle and distribute the meat to the poor and their families. 
 
 A native of Indiana, Peter Kassig founded Special Emergency Response and Assistance, a nongovernmental organization aiding Syrians fleeing the civil war there. 
 
 From 2012, he delivered food and medical supplies within and outside Syria and provided trauma care and training, his family said. 
 
 Soldier, helper, captive 
 
 Kassig's journey began when he joined the U.S. Army Rangers in 2006 and deployed to Iraq in 2007. He was honorably discharged for medical reasons after a brief tour and returned to the United States to study political science and train for 1,500-meter races. But something wasn't right. 
 
 "I was going to school with kids who look the same, were the same age as me, but we weren't the same," he said in an interview with CNN in 2012. "I wanted more of a challenge, a sense of purpose." 
 
 In 2010, Kassig took time off and began his certification as an emergency medical technician. 
 
 In the two years that followed, he fell in love, got married and quickly divorced. Devastated and heartbroken, he went back to school, but he couldn't shake his depression. 
 
 "I needed a game changer," he said. 
 
 He eventually traveled to Lebanon and founded SERA to deliver food and medical supplies to swelling refugee camps. 
 
 On October 1, 2013, he was "detained" on his way to Deir Ezzor in eastern Syria, his family said. 
 
 "Peter really believed that an individual can make a difference in the world through their love and compassion and intelligence," said Margaret Brabant, Kassig's college adviser and a professor at Butler Univeristy in Indianapolis. "... That is the message that I think Peter would want me to convey." 
 
 Hostages tortured before beheadings
– ISIS has beheaded another hostage, but while the outcome is grimly familiar, analysts say the video revealing the death of Peter Kassig has differences that hint at serious problems for the militant group. Unlike four earlier videos showing the execution of Western hostages, the quality is poor, Kassig is not seen reading a statement, and no other hostage is displayed. Instead, only the American's severed head is shown. Analysts suspect that the threat of airstrikes stopped the militants from being able to film outside for long. "The likeliest possibility is that something went wrong when they were beheading him," an expert at the Foundation for Defense of Democracies tells the New York Times. Another possibility, he says, is that Kassig resisted and the "media-savvy" militants were unable to get the video they wanted. Other analysts speculate that the hostage—who converted to Islam while in captivity—may have chosen to recite quotes from the Koran instead of his captors' script. More: Kassig, a former US Army Ranger, founded an organization to aid refugees from the Syrian civil war. His parents say they are heartbroken by the killing but incredibly proud of his work, the AP reports. He "lost his life as a result of his love for the Syrian people and his desire to ease their suffering," his parents, who live in Indianapolis, said in a statement. The latest ISIS video, which also shows the execution of 18 Syrian captives in "revolting, lingering detail," is also different because it shows the faces of many militants and gives a specific location in Syria, notes BBC security correspondent Frank Gardner. He calls Kassig's execution an "act of desperation" carried out by the group because it is unable to fight back against coalition airstrikes. With Kassig dead, ISIS' only remaining American hostage is a 26-year-old woman, security officials tell the Daily Beast. Like Kassig, she was kidnapped while carrying out aid work. Her name has not been made public and officials say it is significant that she doesn't appear in the group's latest video—and while it's not clear what the militants have planned for her, even ISIS is likely to carefully consider the public reaction to killing a female Western captive on camera.