MI5 and police had at least a dozen contacts with the man identified yesterday (Thursday) as Jihadi John who was able to flee Britain for Syria, it emerged last night.
The security services made a botched attempt to "turn" Mohammed Emwazi after he was first intercepted when they feared he was trying to join a Somali terror group six years ago.
However, Emwazi, who grew up in west London and is likely to have been radicalised in this country, rejected the advances and slipped out of the country, despite being on a terror watch list, to become one of the world's most wanted men. The 26-year-old computer programmer has now murdered at least five Western hostages.
Last night, the daughter of one of his victims, questioned how he was able to slip through the net and the Security Service is expected to face a parliamentary inquiry into their contacts with him and whether more could have been done to stop him. The case has echoes of fanatic Michael Adebolajo who was approached by and known to MI5 before going on to murder Drummer Lee Rigby in a London street in 2013.
Intelligence agencies in the UK and America had suggested for several months that they knew the killer's true identity but it was a closely guarded secret. It is understood they only knew definitely in September.
The hooded Isil killer had been known to MI5 since at least 2009 and had been part of a notorious west London network of fanatics called "The London Boys".
The Security Service and police had questioned him or members of his family on a dozen occasions, including an attempt to recruit him, it was claimed. But despite being on a terror watchlist, Emwazi was able to slip out of the UK in 2013 and flee to Syria where he became the infamous and barbaric Isil figure.
Dubbed Jihadi John, Emwazi became the face of Isil brutality, responsible for guarding the terror group's western hostages and handled negotiations with their families before murdering them in a series of horrific videos posted on the internet. He was filmed murdering David Haines, a Scottish aid worker, and Alan Henning, a taxi driver from Manchester who travelled to Syria to help refugees.
Bethany Haines, David's daughter, last night said that she would not rest until there was a "bullet between his eyes" as she questioned how he was allowed to leave the country.
She told ITV News: "There should have been more security in airports to stop people doing that and definitely for him, obviously he's part of a terrorist group and is out to kill hundreds of people and it's not right. They need to be monitoring airports more clearly. They need to be asking more security questions. Why are people going to Turkey and then getting a connecting flight? It's not right. You don't just go to Syria on holiday."
Sir Menzies Campbell, a member of the parliamentary Intelligence and Security Committee (ISC), which examines the activities of the spy agencies, said the committee was likely to seek answers from intelligence chiefs.
Emwazi has claimed he was placed on a terror watch-list in 2009 amid concerns that he was trying to join al-Shabaab, a terror group based in Somalia, after being stopped with two friends in Tanzania
They were removed to Schipol Airport in Holland where he was questioned by an MI5 agent called "Nick", according to a detailed version of events he gave to Cage, a controversial human rights groups.
He claimed Nick told him: "You've got the whole world in front of you; you're 21 years old; you just finished Uni - " why don't you work for us?" He claimed that after he rejected the offer he was told: "You're going to have a lot of trouble... you're going to be known...you're going to be followed... life will be harder for you."
According to his account, Emwazi was stopped again when he returned to Dover the next day and told he was on a terror watchlist.
Over the next four years he claims he or his family were approached or questioned on numerous occasions and he was stopped from trying to leave the UK on at least three occasions. On the last attempt, in early 2013, he had even changed his name to Mohammed al-Ayan. However, just a week later he managed to slip out of the country and head to Syria.
Court documents seen by The Daily Telegraph reveal that Emwazi was part of an established network of extremists based in West London, referred to as the "The London Boys" and well-known to the security services. A number have gone on to fight in Syria, where at least one has been killed. They were originally trained by the al-Shabaab militant group in Somalia.
The legal document from 2012 states that they were part of "a network of United Kingdom and East African-based Islamist extremists involved in providing funds and equipment to Somalia for terrorism-related purposes and helping individuals travel from Britain to Somalia to undertake terrorism-related activity."
The Ladbroke Grove fighters have been linked to the men behind the failed July 21 bombing of 2005, two of whom were arrested during police raids in Notting Hill and nearby North Kensington, close to Emwazi's family home. Ibrahim Magag, another member of the group, is currently on the run after fleeing a court order on his movements by simply removing an electronic monitoring tag and vanishing in a black cab.
In Syria, Jihadi John is believed to head a group of British fanatics dubbed "The Beatles" responsible for murdering a number of Western hostages, including the two Britons and three Americans.
Scotland Yard and Downing Street refused to confirm whether he was the suspect.
Emwazi's parents, Jasem, 51, and Ghaneya, 47, came to London from Kuwait in 1993 when he was six years old in the aftermath of the Gulf War.
The family moved to Maida Vale in West London, where they eventually rented a modest house.
It is thought that Emwazi and his siblings went to the local secondary school, Quintin Kynaston in St
John's Wood, a popular and successful academy. In 2006 Emwazi gained a place on a computer programming course at Westminster University, which has faced questions about links between its student union and extremists.
Emwazi, although by now devout, insisted that he was not a radical at this time and was said to be an occasional worshipper at a mosque in Greenwich, south east London.
He graduated in his early 20s and was described as a "polite" young man who liked to wear stylish western clothes. He had by this stage grown a beard and was "mindful of making eye-contact with women".
One of Emwazi's former teachers told Channel 4 News: "He was a diligent hard working lovely young man, responsible, quiet. He was everything you could want a student to be. I'm just absolutely shocked that it appears to be him."