London: A second British voice has been identified in the disturbing video of an American hostage's beheading released by the Islamic State militants, according to a latest scientific analysis.
The words "Death to them" and "Yeah" can be heard off camera in the recording of US journalist Steven Sotloff's last moments, a study by The Times claims.
A leading audio expert said he was certain that the background voice did not belong to the main militant, dressed in all black and wielding a knife and appears on camera with the kidnapped journalist.
His role in Sotloff's murder, and the threat to kill a British hostage has triggered an international manhunt.
Sotloff's beheading was the second such execution of a US journalist within a fortnight after James Foley.
"Some 1.8 seconds after the final words ["leave our people alone"] of the speaker dressed in black, a background voice makes a short utterance consistent with the phrase in English: 'Death to them'," said a report by the expert, who was commissioned by the newspaper to analyse the Sotloff video and the earlier online footage of James Foley's murder.
Offering fresh analysis of the fighter in the recordings, dubbed Jihadi John, the expert said he believed him to be under 30.
English appeared to be his first language, with an accent from the south-east of England, but he pronounced certain words, such as Iraqi place names, in a way that could indicate his parents or grandparents came from the Middle East.
Some 500 British fighters are estimated to have travelled to Syria, and recently to Iraq, to join the IS.
Overall 12,000 foreign fighters are believed to be in the region, according to London-based International Centre for the Study of Radicalisation (ICSR).
This is the biggest such mobilisation since the Afghan war of the 1980s.
The IS aims to set up a caliphate -- an Islamic form of government last seen under the Ottoman Empire -- extending from Aleppo in northern Syria to Diyala province in eastern Iraq.