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. ||||| BEIRUT (AP) — The Islamic State group has beheaded Peter Kassig, releasing a video Sunday showing a masked militant standing over the severed head of a man it said was the former U.S. Army Ranger-turned-aid worker, who was seized while delivering relief supplies in Syria last year. 
 
 This still image taken from an undated video published on the Internet by the Islamic State group militants and made available, Sunday, Nov. 16, 2014, purports to show extremists marching Syrian soldiers... (Associated Press) 
 
 This undated photo provided by the Kassig Family shows Peter Kassig delivering supplies for Syrian refugees. A new graphic video purportedly produced by Islamic State militants in Syria released Sunday... (Associated Press) 
 
 In this undated photo provided by the Kassig family, Peter Kassig, is shown with his maternal grandparents. His grandfather, a co-founder of Christians for Peace and Justice in the Middle East, was an... (Associated Press) 
 
 FILE - In this August 2013 file photo provided by the Kassig Family, Peter Kissig, who friends and family say changed his name to Abdul-Rahman Kassig, right, works as a medic to help a wounded man near... (Associated Press) 
 
 FILE - This undated file photo provided by the Kassig Family shows Peter Kassig standing in front of a truck filled with supplies for Syrian refugees. A new graphic video purportedly produced by Islamic... (Associated Press) 
 
 President Barack Obama confirmed Kassig's slaying after a U.S. review of the video, which also showed the mass beheadings of a dozen Syrian soldiers. 
 
 The 26-year-old Kassig, who founded an aid group to help Syrians caught in their country's brutal civil war, "was taken from us in an act of pure evil by a terrorist group that the world rightly associates with inhumanity," Obama said in a statement. 
 
 He denounced the extremist group, which he said "revels in the slaughter of innocents, including Muslims, and is bent only on sowing death and destruction." 
 
 The slain hostage's parents, Ed and Paula Kassig, said they were "heartbroken" by their son's killing, but "incredibly proud" of his humanitarian work. 
 
 Kassig "lost his life as a result of his love for the Syrian people and his desire to ease their suffering," the parents said in a statement from Indianapolis, where a vigil was held Sunday for the slain American. His parents attended the vigil. 
 
 With Kassig's death, the Islamic State group has killed five Westerners it was holding. American journalists James Foley and Steven Sotloff were beheaded, as were British aid workers David Haines and Alan Henning. 
 
 Unlike previous videos of slain Western hostages, the footage released Sunday did not show the decapitation of Kassig or the moments leading up to his death. 
 
 "This is Peter Edward Kassig, a U.S. citizen ... who fought against the Muslims in Iraq," said the black-clad militant, who spoke with a British accent that was distorted in the video, apparently to disguise his identity. Previous videos featured a militant with a British accent that the FBI says it has identified, though it hasn't named him publicly. 
 
 The footage released Sunday identifies the militants' location as Dabiq, a town in northern Syria that the Islamic State group uses as the title of its English-language propaganda magazine and where they believe an apocalyptic battle between Muslims and their enemies will occur. 
 
 The high-definition video also showed the beheadings of about a dozen men identified as Syrian military officers and pilots, all dressed in blue jumpsuits. The black-clad militant warns that U.S. soldiers will meet a similar fate. 
 
 "We say to you, Obama: You claim to have withdrawn from Iraq four years ago," the militant said. "Here you are: You have not withdrawn. Rather, you hid some of your forces behind your proxies." A U.S.-led coalition is targeting the Islamic State group in airstrikes, supporting Western-backed Syrian rebels, Kurdish fighters and the Iraqi military. 
 
 Kassig, who served in the U.S. Army's 75th Ranger Regiment, a special operations unit, deployed to Iraq in 2007. After being medically discharged, he returned to the Middle East in 2012 and formed a relief group, Special Emergency Response and Assistance, to aid Syrian refugees. 
 
 A certified EMT, Kassig had delivered food and medical supplies and provided trauma care to wounded Syrians before being captured in eastern Syria on Oct. 1, 2013. Friends say he converted to Islam in captivity and took the first name Abdul-Rahman. 
 
 In a statement issued as he flew back to Washington from the Asia-Pacific region, Obama said Kassig "was a humanitarian who worked to save the lives of Syrians injured and dispossessed" by war. The president offered prayers and condolences to Kassig's family. 
 
 "We cannot begin to imagine their anguish at this painful time," he said. 
 
 Burhan Agha, a Syrian who worked with Kassig in Lebanon, wept when recounting his friend's humanitarian work. 
 
 "If I could apologize to each American, one by one, I would, because Peter died in Syria, while he was helping the Syrian people," Agha told The Associated Press by telephone from Switzerland, where he is seeking asylum. "Those who killed him claimed to have done it in the name of Islam. I am a Muslim and am from Syria. ... (His killers) are not Muslims." 
 
 British Prime Minister David Cameron said he was "horrified by the cold-blooded murder," saying that the Islamic State group had "again shown their depravity." 
 
 In previous videos showing the beheadings of the two American journalists and two British aid workers, the hostages were shown kneeling in orange jumpsuits as they were forced to make speeches before their killer lifted a knife to their throats. 
 
 The latest video did not show Kassig being beheaded. And unlike previous videos, it did not show other Western captives or directly threaten to behead anyone else. It also had lingering close-ups on some militants' exposed faces, a few of whom appeared to be foreigners. 
 
 The video appeared on websites used in the past by the Islamic State group, which now controls a third of Syria and Iraq. 
 
 The terror group still holds other captives, including British photojournalist John Cantlie, who has appeared in several videos delivering statements for the IS, likely under duress, and a 26-year-old American woman captured last year in Syria while working for aid groups. U.S. officials have asked that the woman not be identified out of fears for her safety. 
 
 The video appeared to be part of continuous efforts to strike at the U.S., which is leading an aerial campaign against the group that began in August in Iraq and spread to Syria the following month. 
 
 The video came two days after a recording by the group's leader, Abu Bakr al-Baghdadi, was uploaded to the Internet. The militant leader warned that the U.S.-led coalition's campaign had failed and it would eventually have to send ground troops into battle. 
 
 The group has declared a self-styled Islamic caliphate in areas under its control, which it governs according to its violent interpretation of Shariah law, including massacring rebellious tribes and selling women and children of religious minorities into slavery. 
 
 The group's militants have also beheaded and shot dead hundreds of captives, mostly Syrian and Iraqi soldiers, during its sweep across the two countries, and has celebrated its mass killings in extremely graphic videos. 
 
 The Islamic State group has its roots in al-Qaida's Iraqi affiliate but was expelled from the global terror network over its brutal tactics and refusal to obey orders to confine its activities to Iraq. It became even more extreme amid the bloody civil war in neighboring Syria and grew strong enough to launch a lightning offensive across Iraq. 
 
 Syria's war began as an uprising against President Bashar Assad. Activists say that conflict has killed more than 200,000 people. 
 
 ___ 
 
 Associated Press writers Julie Pace in Brisbane, Australia, David Aguilar in Detroit, Jon Gambrell in Cairo, Vivian Salama in Baghdad and Josh Lederman aboard Air Force One contributed to this report. ||||| 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.
– 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.