Mohammed Emwazi or also known as 'Jihadi John'. Photo / AP
Mohammed Emwazi, the Isis extremist known as "Jihadi John", was able to flee Britain and the scrutiny of the security services despite being a member of a terrorist cell known to have links to the failed 21/7 attacks on London in 2005.
One leading member of Emwazi's network had a telephone conversation on the day of the attacks with Hussein Osman, who was later jailed for life for placing an explosive at Shepherd's Bush Tube station.
The security services were also aware that associates of the 12-strong West London terror group had joined the four 21/7 bombers at a training camp in Cumbria a year before the attempt to bring carnage to London's streets.
The revelations, contained in court documents, raise urgent questions over how Emwazi was able to evade surveillance, slip out of the country in 2013 using false papers and re-emerge in Syria a year later to become the world's most wanted terrorist.
Not only was Emwazi a "person of interest" for MI5 as a member of a London jihadi cell set up in 2007 to recruit for al-Shabaab, an al-Qaeda affiliate, but at least one member of his network had a connection with one of the most infamous crimes in British history.
The failed 21/7 attacks came a fortnight after four men blew themselves up on Tube trains and a bus, killing 52 people and injuring more than 700 others, the worst terrorist atrocity committed on British soil.
MI5 had been aware of Emwazi for six years before he appeared on a hostage video for the first time in August 2014, but appears to have been unable to control the network of which he was a part.
It is understood that three members of Emwazi's network had been subject in 2011 to control orders brought in by the last Labour Government, which meant they had to live outside of London.
However those control orders were disbanded by the coalition; the men were instead subject to TPIMs - terrorism prevention and investigation measures - which allowed them to return to London and re-engage with Emwazi.
Two of the men on these weakened orders later absconded. Emwazi fled to Syria shortly afterwards.
A former deputy chief of MI6, Nigel Inkster, said it had now become clear that the previous control order regime had been a better way of monitoring and controlling subjects.
"Control orders seem to be rather more effective than what has replaced them. They [the Government] need to be careful about coming up with new measures of the TPIMs variety which clearly haven't been wildly successful. The problem with UK counter-terrorism legislation over the past decade is that it has become a patchwork of knee-jerk responses to specific events, rather than something that has really been thought through."
The Daily Mail reported that Emwazi was once part of a terrorist unit tasked by Osama bin Laden with launching atrocities in Britain.
He was a member of a "sleeper" cell dubbed the London Boys, which included three operatives allegedly trained at an al-Qaeda camp in Somalia. All three were close associates of Emwazi. Details of Emwazi's involvement in the terror cell emerged during a "control order" hearing at the High Court in London in 2011.
Isis fanatic knew he was being shadowed by MI5
The Isis killer known as "Jihadi John" revealed that he knew British security services were closing in on him and that he was a "dead man walking" in emails to a Mail on Sunday journalist.
His emails were sent before he left Britain to join Isis (Islamic State) in Syria.
At the time, Mohammed Emwazi, the man now unmasked as the knife-wielding fanatic, was claiming to be an innocent victim of MI5 persecution.
Emwazi, who would go on to orchestrate at least six hostage murders in Syria, said the harassment affected him so badly he was contemplating suicide.
His emails to Robert Verkaik in December 2010 and 2011 offer an insight into his state of mind. Some verge on the paranoid, with complaints that he is being shadowed by intelligence officers.
A few months before he contacted Verkaik, Emwazi was stopped at Heathrow and prevented from flying to Kuwait, where he was born.
He claimed he was interrogated by an aggressive officer who threw him against a wall, grabbed his beard and choked him. He complained to the Independent Police Complaints Commission.
He then met Verkaik, later sending him emails chronicling his alleged victimisation. In one, he recounts what he suggests was a sinister encounter with an MI5 agent.
Having advertised his laptop on classified adverts website Gumtree, he went to meet a prospective buyer near his West London home.
He wrote, ungrammatically: "When I sell anything via internet i always only write my surname in the ad ... I went to meet that person ... so that he could have a look at the laptop & if it satisfied him then he would buy it ...
"That person to my surprise didn't even bother looking to see of the laptop works or not!!! (when you buy something, from someone you've never seen before you most likely would test the product!!) ...
"Anyway, in a matter of seconds, I gave him the laptop (thinking that hes going to test the laptop) & he gave me the money straight-away ... We 'shacked hands' & he said 'nice doing business with you Mohammed'. I NEVER TOLD THIS PERSON MY FIRST NAME!! & I NEVER GIVE OUT MY FIRST NAME!! IT WAS IMPOSSIBLE FOR HIM TO KNOW MY FIRST NAME!!"
He added: "I felt shocked, & paused for a few seconds as he walked away ... I knew it was them!! Sometimes i feel like im a dead man walking, not fearing they may kill me.
"Rather, fearing that one day, I'll take as many pills as I can so that I can sleep for ever!! I just want to get away from these people!!!"
Mohammed Emwazi
*Mohammed Emwazi was a member of a secret Osama bin Laden sleeper cell based in Britain called the London Boys, which planned to carry out atrocities in the West.
*He was involved with a violent street gang who targeted the wealthy residents of Belgravia with stun guns.