The masked Islamic State militant known as “Jihadi John”, who has been pictured in the videos of the beheadings of Western hostages, has been named.
The BBC understands he is Mohammed Emwazi, a Kuwaiti-born British man believed to be from West London, who was known to UK security services.
They chose not to disclose his name earlier for operational reasons.
Emwazi first appeared in a video last August, when he apparently killed the American journalist James Foley.
He was later thought to have been pictured in the videos of the beheadings of US journalist Steven Sotloff, British aid worker David Haines, British taxi driver Alan Henning, and American aid worker Abdul-Rahman Kassig, also known as Peter.
In each of the videos, the militant appeared dressed in a black robe with a black balaclava covering all but his eyes and top of his nose.
Analysis: Dominic Casciani, BBC News
We don’t know when the British or the American security services worked out that the masked man in the killing videos was Londoner Mohammed Emwazi.
But we do know that he was a “person of interest” to MI5 going back to at least 2011 because he features in semi-secret court cases relating to extremism overseas and back in the UK.
Nobody in official security circles is going to comment on what they know and why they know it.
Emwazi has been previously described as a member of a network involving at least 13 men from London – and at least two of them were subjected to house arrest control orders or T-Pims. One absconded. The chances of Emwazi ever returning to the UK are vanishingly small.
Speaking with a British accent, he taunted and threatened Western powers before appearing to kill the hostages.
Last month, the militant appeared in a video with the Japanese hostages Haruna Yukawa and Kenji Goto, shortly before they were killed.
Friends of Emzawi told the Washington Post that he was from a well-to-do family and that he studied computer programming at university.
He is believed to be an associate of a former UK control order suspect, who travelled to Somalia in 2006 and is allegedly linked to a facilitation and funding network for Somali militant group al-Shabab.
The Washington Post said he was believed to have travelled to Syria around 2012 and later joined Islamic State, which has declared the creation of a “caliphate” in the large swathes of Syria and neighbouring Iraq it controls.
British police declined to comment on the reports.
Commander Richard Walton, head of the Metropolitan Police’s Counter Terrorism Command, said: “We have previously asked media outlets not to speculate about the details of our investigation on the basis that life is at risk.
“We are not going to confirm the identity of anyone at this stage or give an update on the progress of this live counter-terrorism investigation.”