There's been no official confirmation yet, but various sources have told both CBS News and the British media that a masked man in the latest ISIS propaganda video is suspected to be Siddartha Dhar. He is being called the new "Jihadi John" by the British media.
Dhar is from London, and was raised a Hindu but converted to Islam as a young man, reports CBS News correspondent Elizabeth Palmer. He eventually joined a banned radical Islamic group, Al Muhajiroun, led by extremist Anjem Choudary.
In 2014 he was arrested with Choudhary on suspicion of encouraging terrorism, but released for lack of evidence. He immediately made a break for Syria and joined ISIS, tweeting, "What a shoddy security system Britain must have to allow me to breeze through Europe to the Islamic State."
Later, using his ISIS name Abu Rumaysah, he posted a photo of himself holding a gun and his fifth child.
In the recent ISIS video, which apparently shows the execution of five men, the man thought to be Dahr is masked. In it, he taunts the British government.
Dahr's sister said she can't be sure the masked man is her brother.
"I think it's a bit hard to say, given what I've seen. I'm not entirely convinced that it is. My honest opinion is that it might not be," Konika Dhar said.
But many other people who knew Dhar think it probably is.
One of the hundreds of British citizens now in Syria, including a little boy who appears at the end of the video. He's though to be about four years old.
To establish his identity conclusively, British intelligence services will examine as much as they can of his face behind the mask and compare his voice with samples they already have.