LONDON - The BBC said on Thursday it had learned that the "Jihadi John" suspect who has featured in several Islamic State beheading videos is Mohammed Emwazi from London.
Earlier, the Washington Post newspaper had also identified Emwazi and said he was a Briton from a well-to-do family who grew up in West London and graduated from college with a degree in computer programming.
Police declined to comment on the reports.
"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," said Commander Richard Walton of the Metropolitan Police's Counter Terrorism Command in a statement.
In videos released by Islamic State (IS), the masked, black-clad militant brandishing a knife and speaking with an English accent appears to have carried out the beheadings of three Americans and two Britons..
"His real name, according to friends and others familiar with his case, is Mohammed Emwazi, a Briton from a well-to-do family who grew up in West London and graduated from college with a degree in computer programming," the Post said.
In each beheading video, he is dressed entirely in black, a balaclava covering all but his eyes and the ridge of his nose. He wears a holster under his left arm.
Hostages gave him the name John as he and other Britons had been nicknamed the Beatles, another was dubbed George.
The paper said he had been born in Kuwait, was raised in a middle-class neighbourhood in London and occasionally prayed at a mosque in Greenwich, southeast London.
The Post quoted friends of Emwazi, who spoke on condition of anonymity, as saying they thought he had started to become radicalised after a planned safari in Tanzania following his graduation from the University of Westminster in London.
They said Emwazi and two friends - a German convert to Islam named Omar and another man, Abu Talib - never made it to the safari. On landing in Dar es Salaam, in May 2009, they were detained by police and held overnight before eventually being deported, they said.
No comment was immediately available from the University of Westminster.
The Post said counterterrorism officials in Britain detained Emwazi in 2010, fingerprinting him and searching his belongings.
Families of the murdered hostages said they looked forward to seeing Emwazi brought to justice.
In the videos posted online, he appears dressed all in black with only his eyes exposed, brandishing a knife while launching tirades against the West.
A Washington Post report citing friends, a leading think-tank researching foreign jihadists and a British security official quoted by the New York Times identified Emwazi as the executioner.
However London's Metropolitan Police dismissed the reports as "speculation" and said it was "not going to confirm his identity" to protect human lives while the US National Security Council said it would neither confirm nor deny the reports.
The International Centre for the Study of Radicalisation at King's College in London said it believed the identity "to be accurate and correct".
"We're pretty confident that the right individual has been named," Shiraz Maher, a senior research fellow at the centre, told AFP.
He believed the leak had come from the United States and pointed out that "there are no further Americans being held hostage by Islamic State".
"I think the US chose to put this out," he said.
'Bullet between his eyes'
The family of Sotloff, an American-Israeli journalist murdered by the Islamic State group, said they hoped establishing the identity of the killer would bring him closer to facing justice.
"The Sotloff family was informed of John's identity. This is one step on a long road to bringing him to justice," said Barak Barfi, the Sotloff family's spokesman, in a statement.
"If indeed Mohammed Emwazi is the man who executed Steve, the Sotloffs have full faith that the American intelligence community and law enforcement agencies will apprehend him.
"They look forward to the day that John will be prosecuted and convicted for the crime of executing Steve." The daughter of aid worker Haines told ITV News that her family would "feel closure and relief once there's a bullet between his eyes".
'Beautiful young man'
Cage, a civil rights group that was in contact with Emwazi for several years over his alleged harassment by British security services, said that while not 100 percent certain, it believed it was him.
Cage's research director Asim Qureishi described Emwazi as a "beautiful young man" who had been alienated by his treatment at the hands of the British security services.
Cage published correspondence with Emwazi in which he alleged that a British MI5 secret service agent named "Nick" tried to recruit him while interrogating him at Amsterdam's Schiphol Airport in 2009.
Emwazi said he was returning with two friends after they were expelled from Tanzania, accused of trying to join Islamist militants in Somalia but on a trip that he said was a safari holiday after finishing university.
"Why don't you work for us?" Emwazi quoted "Nick" as telling him. After refusing, he said the officer told him: "You're going to have a lot of trouble, you're going to be known, you're going to be followed." After being refused entry to Kuwait three times, Emwazi left his London home in 2013 and four months later police told his family he had entered Syria, according to Cage.
The emails appear to point to growing radicalisation - he finished one in 2010 saying: "May Allah get rid of the oppressors i.e. security agents".
Polite and stylish
Emwazi, said by Cage to be 26, was identified to the Washington Post by friends and others familiar with the case, with one acquaintance telling the paper: "I have no doubt that Mohammed is Jihadi John".
Emwazi is from a middle class family and earned a degree in computer programming. He is described as being quiet and polite with stylish dress sense. In one email to Cage, he complained about police going through his designer clothes.
Dozens of reporters gathered outside a modern property believed to belong to his family in the northwest London neighbourhood of Queen's Park.
Qureishi, Cage's research director, said the family did not believe the allegations against their son and were in a state of "absolute shock".
The University of Westminster said in a statement that it had a record of a Mohammed Emwazi leaving college six years ago and was setting up a pastoral team to provide advice and support to students.
Maher, the research fellow from King's College, London predicted that Emwazi's apparent unmasking would deal a "psychological blow" to the IS group.
"They'll feel somewhat deflated that someone they wanted to preserve and protect as an asset has been outed in this way but it won't change anything day to day."