The third British man, now identified in an ISIS recruitment video, was a normal lad more interested in football than mosque, his shocked community have said.
Abdul Raqib Amin, who was brought up in Aberdeen, is said to appear in the video for the group Islamic State of Iraq and the Levant (Isis) with Nasser Muthana and Reyaad Khan, both from Cardiff.
He is identified as 'Brother Abu Bara' al Hindi' in the online video which emerged last week.
Wearing dark sunglasses and a jaunty grin, Amin is heard to say: "Are you willing to sacrifice the fat job you’ve got, the big car you’ve got, the family you have? Are you willing to sacrifice this, for the sake of Allah?
"Definitely, if you sacrifice something for Allah, Allah will give you 700 times more than this."
Raqib was educated in Aberdeen after moving from Bangladesh and his family left the Scottish city a couple of years ago, according to the BBC.
A local Muslim who knew Amin told Sky News: "He was more of a lad than a regular attendee at the mosque. He was a happy guy, played football - he was a good player and he supported Aberdeen. I remember him as a hyper person, energetic and loud... not the type of person you'd expect to go and do this."
A leading member of Aberdeen's Muslim community, who did not want to be identified, told the Press Association he was not someone who "stood out in any particular way".
"Obviously the community is in shock, the Muslim community in Aberdeen is mainly made up of oil and gas professionals and students so it's quite small," he said. "You hear about things like this in some cities down south but never in Aberdeen. From what I know the guy moved from Bangladesh and lived here for maybe seven or eight years then moved away about two years ago.
"He must have got his network when he moved away because that environment doesn't exist in Aberdeen. He never stood out in any particular way when he was here, I don't really think he was that regular in the Mosque, he was just a young lad.
"As a community we're in shock and we just hope that the media handle it responsibly, because there can be a backlash to these kind of things and that would be totally wrong."
Ibrahim Alwawi, imam of the Aberdeen Mosque and Islamic Centre, told the BBC: ''We, as the Muslim community in the city of Aberdeen, are shocked like everyone else. ''We are co-operating with the authorities as we usually do.''
The father of Nasser Muthana said his son had "betrayed'' his country. Ahmed Muthana believes his other son, 17-year-old Aseel, is also in the Middle East and said they were "brainwashed" in the UK.
Internet video-streaming sites such as YouTube are being pressed to take down the film by the Government.
A No 10 spokeswoman said the Government had already succeeded in removing 15,000 pieces of extremist material from the internet since starting a drive in December to block jihadi terrorists from using online messages to recruit Muslims in Britain to their cause.
The spokeswoman told a regular Westminster media briefing today: ''We do think it is extremely important to be looking at what there is online and working with the internet industry to remove terrorist material hosted in the UK or overseas.
''Since December we have removed over 15,000 pieces of terrorist-related content from the internet... That reflects the scale of the problem, but it also reflects the good relationship we have with the industry."
Sheikh Zane Abdo, imam of the South Wales Islamic Centre, said he feared widespread publicity given to the video would encourage other ''susceptible'' young men to travel to Syria to fight - fears that were echoed by senior counter-terrorism police officers.
The imam said: ''I guarantee that many young people who are very susceptible to this type of message will have watched that video and maybe have been encouraged to now go and follow in the footsteps of Nasser and his brother, which is a real problem, the fact that a platform has been given to this video that really shouldn't have been given.''
Sir Peter Fahy, lead on the Prevent counter-terrorism strategy for the Association of Chief Police Officers, warned that the video made the young men's trip look like a ''Boy Scout camp'' when the reality was ''very brutal, very callous''.
''The Government does have some funding and is putting material on the internet but really we need the whole of the community to counter this narrative,'' he said.
''The trouble with this Isis video is it makes it look like a Boy Scout camp going out there, when in fact what they are calling for is Muslims to go out to kill fellow Muslims, often in cold blood, with summary executions of conscript soldiers and police officers.
"The trouble with that particular video is it makes it look very glamorous, that they are going on an adventure, when the reality is actually very brutal, very callous.''
The warnings about the impact of the video came as security experts in the UK declared that the repercussions of Syria and the rise of Islamic extremism at home will be felt for ''many years'' to come.
Richard Barrett, a former head of counter-terrorism at MI6, estimated that ''possibly up to 300 people have come back to the UK'' already, and warned that intelligence services faced an ''impossible'' task in trying to track them.
He said: ''Clearly they'll have to prioritise and they'll have to choose those that they think are likely to pose the greatest risk.
''Beyond that I think they'll have to rely very much on members of the community and other people expressing their concern and worry about the behaviour of perhaps their returned friend or family member.''