The British jihadist suspected of murdering American journalist James Foley has been identified, the Sunday Times reports. Government sources said that security agencies MI5 and MI6 have worked out the identity of the masked fighter, who is said to be known as “Jihadi John” to fellow Islamists, although they have so far declined to give the man’s identity.

Despite their reluctance to announce the killer’s identity, one key suspect is 23-year-old Abdel-Majed Abdel Bary, who previously lived with his family in their £1 million home in London’s wealthy Maida Vale district.

Meanwhile, the Sunday Telegraph says that intelligence agencies are investigating footage of two jihadists taking part in the execution of a Syrian soldier to see if one of the men is the same person who killed Foley. The video, posted to Instagram, shows the soldier crouching in a field before being shot in the back of the head. His body is then shot with an automatic rifle by a second man.

The Telegraph says that one of the British men is wearing a similar black robe to “Jihadi John” and is of a similar height and build. Like “Jihadi John”, he also appears to be left-handed.

Researchers from the International Centre for the Study of Radicalisation (ISCR), which is based at London’s Kings College, told the paper that the British fighters are believed to be part of a group called Rayat al Tawheed, which has close links to ISIS.

A security source said: “We are considering all evidence from the internet to establish who killed James Foley. We can’t afford to rule anything out. But at the same time nothing can be taken at face value.”

Intelligence agencies are using various sophisticated tools to analyse the extremist videos, including supercomputers that can help identify and match voices in different recordings. They are also trying to work out what sort of equipment was used to record the videos. James Foley’s murder was recorded on a high-quality camera, with sophisticated editing software, making it easier to identify the killer’s voice.

However, investigators have not ruled out that the killer’s voice could have been dubbed into the footage, meaning that the man heard speaking would not be the same as the man who carried out the murder.

ISIS posted the video of Foley’s murder last week, sparking international outrage, as well deep concern in the UK over the killer’s apparent British accent. The British government believes there to be about 500 Britons fighting in Syria and Iraq, raising fears that battle hardened jihadists could try to return to the UK and spread terror.