The masked militant who acted as the spokesman for ISIS in a new propaganda video is believed to be Siddhartha Dhar, also known as Abu Rumaysah, according to U.S. law enforcement sources who were briefed by U.K. officials.

Authorities suspect that he is a British Muslim convert from London who once touted rentals of children's bouncy houses, according to multiple reports. He is thought to have left the U.K. in late 2014 or 2015.

NPR's Dina Temple-Raston reports that he was part of al-Muhajiroun, a radical Islamist group now banned in the U.K.

"He is an acolyte of Anjem Choudary, a controversial radical cleric in the United Kingdom who led al-Muhajiroun," she says, adding: "His family — four children and his wife — are believed to have gone with him to Syria."

Dhar, 32, was borna Hindu and converted to Islam after marrying a Muslim, according to the BBC and other news outlets. Also known as Abu Rumaysah, Dhar absconded from Britain while he was on bail for terrorism charges.

Recapping what's known about the suspect, Larry Miller reports for our Newscast unit, "32-year-old Siddhartha Dhar was a 'moon bounce' salesman from East London before his conversion to Islam."

Before he fled Britain, Dhar had become a public advocate for life under ISIS, promoting the group in panel discussions and TV interviews. He later released a pamphlet titled "A Brief Guide to the Islamic State [2015]," which attempted to lure Westerners with everything from candy to a Mediterranean climate with this promise: "'If you were worried about leaving behind your local Costa coffee then you will be happy to know that the caliphate serves some of the best lattes and cappuccinos around."

The man suspected to be Dhar plays a key role in an ISIS video released over the weekend that shows five people being executed with pistols. Much like his predecessor "Jihadi John" — another Brit, who the U.S. says was killed in a drone strike in November — the man wears a balaclava mask as he issues threats to Britain and belittles Prime Minister David Cameron.

A Twitter account for Abu Rumaysah has been suspended, but a YouTube account in that name remains active, with 10 posted videos showing Dhar discussing extremism and ISIS in propaganda and TV appearances.

In one interview from August 2014, Dhar professes his affection for ISIS, but he refuses to declare his support for terrorism, citing the threat of arrests.

"The ironic thing is that in this country you've got freedom of speech, but for Muslims, there is no freedom," he said. "What I would say is that I would love to live under the Islamic State, I would love to live under the Shariah — and I hope one day, that Britain gets to live under the Shariah as well."

The new ISIS video also features a young boy who speaks with a British accent, wearing camouflage and a black ISIS headband. Henry Dare of London has said he believes the boy, who's around 5 years old, is his grandson.

In the video, the boy states, "We will kill the kuffar over there" — referring to nonbelievers.

Dare's daughter, Grace, converted to Islam from Christianity and took the name Khadijah Dare. She moved to Syria in 2012 and married Swedish jihadist Abu Bakr, according to ITV News.

Like Dhar, she later posted photos of herself holding an AK-47 rifle on social media.

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