The masked gunman in the latest Islamic State propaganda video is believed to be a British Muslim who was well-known in radical Islamist circles and appeared on TV debate programs espousing his extremist views.
Siddhartha Dhar frequently went on camera to defend the militant group and spoke as an expert on sharia law, or Islamic law, during live news segments. He is believed to have fled to Syria in 2014 while on police bail and is now being dubbed the "new Jihadi John" by British media. The nickname refers to London-raised Mohammed Emwazi, who appeared in Islamic State execution videos. Emwazi was killed in a U.S. drone strike in November.
In the latest video released by Islamic State during the weekend, a man wearing combat fatigues and holding a handgun is seen standing in front of five accused "spies." He speaks fluent English with a British accent and taunts Prime Minister David Cameron as a "slave of the White House" and an "insignificant leader." The speaker also threatens to invade Britain and impose sharia law.
"How strange it is that a leader of a small island threatens us with a handful of planes," he says, referring to Britain's recent vote to join U.S.-led airstrikes against Islamic State militants in Syria.
The masked man then appears to shoot one of the men in the head.
Dhar, believed to be in his 30s, grew up in a Hindu family in Walthamstow, East London, but converted to Islam. He goes by the name Abu Rumaysah and has published an online guide to living as part of Islamic State.
His sister, Konika, told the BBC this week that she was in a state of denial that this could be her brother but said the voice sounded familiar, although she was not entirely sure.
"I believe the audio to resemble, from what I remember, the voice of my brother," she said. "It's been very hard for me just to deal with the loss of my brother because I still classify him as my brother … I just don't want to believe he's out there and he's become this new person."
When not espousing radical Islamist views and attending demonstrations, Dhar reportedly worked as a bounce house salesman. He often took part in debate programs and would also post videos online and stand outside mosques on Friday afternoons searching for new followers.
"Now that we have this caliphate I think you'll see many Muslims globally seeing it as an opportunity for the Koran to be realized," he said in an interview on the BBC. "As a Muslim I would like to see the UK governed by the sharia. It is far superior to democracy. I don't really identify myself with British values. I am Muslim first, second and last."
Dhar was arrested in September 2014 on suspicion of encouraging terrorism and being a member of the banned militant group Al Muhajiroun. He was granted bail on condition he surrender his passport, but instead of doing so, he reportedly swiftly boarded a bus from London to Paris with his wife and four children.
The family later traveled to Syria, where Dhar posted a photograph of himself posing with a gun in one hand and his newborn baby in the other.
He also goaded the authorities by tweeting: "What a shoddy security system Britain must have to allow me to breeze through Europe to the Islamic State."
It took more than a month for authorities to write to Dhar asking him why he had not handed in his passport. The apparent security lapse has caused a political row in Britain with Home Secretary Theresa May under pressure to launch an inquiry into the circumstances of Dhar's disappearance.
Cameron described the video as a "desperate" move from a group that was losing territory and public sympathy.
"This again shows what an appalling organization we are up against," the prime minister told reporters. "I know that Britain will never be cowed by this sort of terrorism. Our values are so much stronger than theirs. It may take a very long time, but they will be defeated."