Killer in video is called John, the (Black) Beatle
HE IS left-handed, speaks with a British accent and was captured on video, ruthlessly beheading American journalist James Foley.
British intelligence agencies say that he is one of a gang of British jihadis known as the "Beatles".
The killer styles himself "John". Along with fellow British fanatics who are called "Ringo" and "Paul", this killer Beatle is said to have guarded non-Syrian hostages captured by the Islamic State in Syria.
He has climbed up the ranks of the militants and was trusted earlier this year to negotiate a hostage exchange.
Security agencies are using advanced voice-recognition techniques to identify "John", who wore Timberland boots, threatened the United States and spoke in an East London accent.
A militant arrested in Syria described "John" as intelligent, well-educated and extremely radical.
The dramatic footage of his act also put the focus on the rising number of Britons who have have been travelling to Syria and Iraq to join hands with the militants.
Experts said that almost 500 British citizens are now jihadist fighters.
Shiraz Maher, of the International Centre for the Study of Radicalisation at King's College London, said British recruits are "among some of the most vicious and vociferous fighters who are out there".
And they are no longer foot soldiers in the battle, but have worked their way up to senior positions in Islamic State.
Expressing his shock at the developments, British Prime Minister David Cameron said that his government was looking at confiscating the passports of those who were planning to travel to Syria to take part in the fighting.
Meanwhile, despite threats from "John" to kill another American reporter being held hostage, US aircraft launched fresh strikes against militants in northern Iraq.
Fourteen of these new strikes were aimed near the Mosul dam, a key facility recaptured from militants earlier this week.
US President Barack Obama emerged briefly from his holiday to hit out at the militants who killed Mr Foley. "People like these ultimately fail...because the future is always won by those who build, not destroy," he said.
Indonesian President Susilo Bambang Yudhoyono called the actions of the militants "embarrassing to the religion".