Hunt is on for suspected British jihadi in James Foley execution videoBy Laura Smith-Spark and Erin McLaughlin, CNNUpdated 8:45 PM ET, Thu August 21, 2014Just WatchedWho is James Foley's executioner?replayMore Videos ...Who is James Foley's executioner? 00:10Story highlightsThe ISIS fighter who talks in the execution video has what sounds like a British accentBritain's counter terrorism police have joined the hunt for the killer of James FoleyThere are an estimated 400-500 British jihadis in the Syria and Iraq regionUK Foreign Secretary: "This is a poison, a cancer, what's going on in Iraq and Syria"An international manhunt is under way for the fighter shown in a video of the beheading of journalist James Foley -- and its focus is on Britain.The Islamic State militant on the video has his face covered, except for his eyes. But he has what sounds like a distinctly British accent.UK media reports are rife with speculation about where he's from. Linguistics experts say his accent indicates he is from southeast England or London, perhaps the capital's East End.As details of the cold-blooded execution of Foley emerged, British Prime Minister David Cameron interrupted his summer vacation to head a meeting of the government's emergency committee, known as COBRA, in London.Just WatchedUncovering intelligence from ISIS videoreplayMore Videos ...Uncovering intelligence from ISIS video 02:05PLAY VIDEOSpeaking to the media, he condemned the killing as "a murder without any justification" and said that while the man has not been identified, "it looks increasingly likely that it is a British citizen."Just WatchedWhy so many jihadists from UK?replayMore Videos ...Why so many jihadists from UK? 06:07PLAY VIDEOJust WatchedSpecial ops were sent to rescue FoleyreplayMore Videos ...Special ops were sent to rescue Foley 02:02PLAY VIDEOOpinion: Why James Foley's murder was a message to BritainA lengthy processWith an estimated 400 to 500 British recruits in Syria and Iraq -- though some believe the number to be much higher -- it may take time to identify the killer.And UK Foreign Secretary Philip Hammond said the government is well aware of the threat these British jihadis pose, at home as well as overseas."We've been saying for a very long time that there are a significant number of British nationals, both in Syria and Iraq, operating with extremist organizations," he said."Many of these people may seek at some point to return to the UK and they would then pose a direct threat to our domestic security. "This is a poison, a cancer, what's going on in Iraq and Syria, and it risks spreading to other parts of the international community and affecting us all directly."Easy recruitsAnalysts who study the Islamic State say they are not surprised by the role played by a Briton in Foley's killing. "The British fighters who have been going out to the Islamic State, who we've been monitoring now for many years, are really wanting to be at the forefront of this conflict," Shiraz Maher, a senior research fellow at King's College London, told CNN. "They're not backseat drivers in any sense."The power of the Internet means radicalization and recruitment of fighters is also alarmingly easy.According to a defector from the ranks of ISIS, the jihadist group runs a series of Internet chat groups to begin the process of indoctrinating and filtering potential recruits from outside Syria.Just WatchedThe lure of jihadismreplayMore Videos ...The lure of jihadism 05:07PLAY VIDEOJust WatchedU.S.: Attempt to rescue Foley failedreplayMore Videos ...U.S.: Attempt to rescue Foley failed 02:35PLAY VIDEOJust WatchedEuropean members ups danger of ISISreplayMore Videos ...European members ups danger of ISIS 01:37PLAY VIDEOCaptors originally asked for huge ransomEuropeans sought afterThe defector, who agreed to an interview with CNN earlier this summer but wanted to hide his identity, said that European recruits were more sought after and treated in a different class by the recruiters."There was special treatment for the Europeans," he said. "One British guy said he was called Ibrahim, then told me he was from Manchester. One asked my emir (his unit's head) if he should fight in his own country, or come to Syria. He was told if God doesn't give you martyrdom in Syria, then he could wage war in his own country."Maajid Nawaz, co-founder and chairman of Quilliam, a London-based counter-extremism think tank, told CNN that British jihadis -- writing on social media websites -- had made plain their intention to carry on their jihad when they return home. Some have posted pictures of themselves posing with homemade bombs.Nawaz said the estimated 500 British fighters in the region equates to roughly one in every 800 Sunni Muslim British men of fighting age.'Fighters don't emerge from a vacuum'"That's a huge proportion of this country's Muslim population who have succumbed to this level of violence," he said."Those fighters don't emerge from a vacuum, they don't just spring up from nothing. There must be some form of residual atmosphere that's prevalent within our communities here that somehow incubates that type of mindset. So it's definitely very worrying for us."There are roughly 3,000 from across Europe and of course we can travel throughout Europe without a visa -- so that means any country can succumb to these kind of attacks as soon as they return home."Other attackersOther Britons have helped carry out brazen attacks in Syria.Just WatchedHagel: ISIS 'beyond a terrorist group'replayMore Videos ...Hagel: ISIS 'beyond a terrorist group' 01:27PLAY VIDEOJust WatchedWill ISIS execution change Iraq strategy?replayMore Videos ...Will ISIS execution change Iraq strategy? 05:52PLAY VIDEOJust WatchedJames Foley: In his wordsreplayMore Videos ...James Foley: In his words 02:25PLAY VIDEOEarlier this year, father-of-three Abdul Waheed Majid is believed to have become Britain's first known suicide bomber there, when he blew up a truck bomb as part of an ISIS assault on an Aleppo prison.The 41-year-old, from Crawley, south of London, told his family he was in Syria as a humanitarian worker -- not as an ISIS fighter. His uncle, Mohammad Jamil, said, "He was a good family man. He had his head in the right place you know. We never thought he was linked to anyone other than his family and doing good deeds."Beheading of American journalist James Foley recalls past horrorsPropaganda valueAnalysts say some of the propaganda value of the Western foreign fighter lies in that contradiction between their past and present identities."In showing a Briton decapitating an innocent civilian American, they've shown that they've deconstructed the boundaries of any former life of this British citizen," said Charlie Cooper, a researcher at the Quilliam Foundation."He has left his country and he has gone to fight for the Islamic State, and in doing so he has completely rejected his former life. He's rejected all ideals that he used to live in and now he's happy to decapitate someone who is unarmed in front of a camera to further the message and threaten the rest of the world, as well as the United States."To break down someone to that level, to brainwash them like that, is immensely powerful."London's Metropolitan Police confirmed Wednesday that its Counter Terrorism Command was investigating the video. Britain's MI5 domestic intelligence agency is also said to be involved in the hunt, as are U.S. authorities.Besides the brutality of his own actions, that potent capacity to radicalize others will only add to the urgency of the hunt for James Foley's killer.READ: ISIS beheading: What should U.S. do?READ: Will anyone stop ISIS?ISISISIS governor killed in airstrikes The latest ISIS-appointed governor of Mosul was killed in coalition airstrikes on Christmas Day, according to Iraqi police. Author's journey inside ISISAuthor Juergen Todenhoefer says ISIS are "more dangerous than people realize."The Pentagon has a new name for ISISThere's yet another new name for ISIS among those fighting against the terror group. Daesh. FBI warns military of ISIS threatThe FBI warns U.S military that ISIS are looking for individuals who may be interested in carrying out attacks on home soil.Iraqi army's 'ghost' soldiersIraq's Prime Minister says there is evidence of 50,000 soldiers being paid while inactive.Pentagon insider may lead war on ISISPentagon insider Ashton Carter is expected to be President Barack Obama's nominee for Defense Secretary.U.S. seeks strategy reviewWolf Blitzer talks to Rep. Ed Royce about the White House's new ISIS strategy that involves removing Bashar al-Assad.Child fighter tormented by ISIS Just two weeks ago, Yasir was regularly strapped into an explosive vest and handed guns and a radio to stand guard at an ISIS base in Syria.Jihadi Janes try to join ISISHow did three U.S. teenagers become radicalized? CNN's Pamela Brown reports.Why is ISIS so attractive to recruits?Reza Aslan examines the appeal of ISIS and why the group is able to successfully attract so many recruits.This is how ISIS indoctrinates kids CNN's Nick Paton Walsh takes a look at how ISIS is using media to desensitize children. Travel ad or pro-ISIS video?A new propaganda video from ISIS features a Canadian ISIS member who died in combat.ISIS: Everything you need to knowExplore CNN's interactive that explains ISIS' roots, what it controls, and where its support comes from.More from europeUK opens inquiry into Russian spy Litvinenko's deathGreek F-16 crashes in Spain during NATO exercise, killing 11Surviving Auschwitz: 'I just wanted to live another day'