London: The key suspect in the hunt for the new "Jihadi John" travelled to Syria with his wife and four children under the noses of the security services, despite being on bail for alleged terrorism offences, it has emerged.
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The family of British Muslim convert, Siddhartha Dhar, said on Monday that the killer seen shooting a prisoner in the head in the latest Islamic State (also known as ISIL or ISIS) video could be the 32-year-old former bouncy castle salesman from east London.
Both his mother and sister said they had watched the video, released by IS on Sunday, and noticed similarities between the voice of the masked jihadi and Dhar.
Dhar, who is also known as Abu Rumasayah, was arrested in September 2014 alongside the preacher Anjem Choudary on suspicion of belonging to the banned group al-Muhajiroun.
Choudary will appear in court on suspicion of terror offences next week, but Dhar will not be in the dock alongside him after fleeing Britain.
Just hours after being granted police bail, Dhar caught a bus to Paris with his family and then travelled on to Syria where he joined IS.
He then taunted the British authorities by boasting of his new life in the self-styled caliphate and posted pictures on Twitter, showing him holding an AK-47 assault rifle in one arm and his baby son on the other.
Voice recognition experts working for the security services were last night urgently scrutinising the IS video amid the suggestion that the Islamist's voice matched that of Dhar.
Meanwhile in other developments:
* A child who also featured in the video was positively identified as the son of jihadi bride, Grace Dare, from Lewisham, south-east London.
* David Cameron, denounced the video as "despicable" but said people should watch it to remind themselves of IS's "ghastly" tactics.
If Dhar's identity in the terrorist outrage is confirmed it will lead to uncomfortable questions for the security services, who allowed him to leave the country just hours after the police granted him bail.
Speaking at the family home, his mother, Sobita Dhar said she could not rule out that the man in the video was her son. She said: "I heard the voice, yes, but I don't know, I'm not sure of the voice. These are the most difficult questions to answer. I just cannot say.
"I'm not sure within myself whether it is the truth or not."
His sister, Konika Dhar, from north London said she did not want to believe her brother could be responsible for the outrage, but conceded the voice on the video "did sound like him".
She said: "I can't believe it. This is just so shocking for me. I don't know what the authorities are doing to confirm the identity, but I need to know if it is." She said he had converted more than 10 years ago, and her memories of her brother are from when they were children and teenagers.
She said: "He was a very pleasant boy, and I know it may be hard to believe but he still is, and I still believe that he still can be that person."
Dhar, who was brought up a Hindu, ran a firm hiring out bouncy castles, before marrying his Muslim wife Aisha and becoming radicalised.
Former neighbours in Walthamstow, east London, claimed Dhar's wife was more devout than him and suggested she may have put him on the path to extremism.
In the months leading up to his arrest Dhar was accused of burning poppies and calling for the imposition of sharia law in Britain.
He was a key member of al-Muhajiroun and offshoot groups such as the Shariah Project, masterminding "roadshows" in London that aimed to recruit troubled youngsters to Islam. In one interview around that time he said: "We believe that whenever the sharia is established, the pure Islamic state maybe in Iraq or Syria, one day the leader will wage jihad and annex Britain into the Islamic state.
"We are not going to forget Europe, we are not going to forget Britain, the armies will be sent here to conquer these lands."
One former neighbour in east London, who asked not to be named, said: "He refused to talk to me - he was quite rude. He converted to marry her - it was her family that were more hardcore." The IS propaganda video was released on Sunday and showed the murder of five Syrian men, who were accused of spying for the British.
In the gruesome 10 and a half minute clip, the men, who are wearing orange jump suits, each confess to passing on information about IS and its operatives. The video then shows the men kneeling in front of five masked gunmen in a desert landscape, before the British Islamist delivers his rant.
Using rhetoric similar to that Dhar has used in the past, the gunman dismissed Mr Cameron as an "imbecile" and said the RAF airstrikes would have no impact against the IS forces.
Dr Frederika Holmes, a forensic speech and voice analyst, said the sound quality would enable a positive identification.