JIHADI John was unmasked hours after releasing his first ISIS execution video after British spooks recognised the veins in his knife-wielding hand.
Analysts at GCHQ also studied the disguised voice with wiretap recordings and quickly identified him as Mohammed Emwazi from London.
Robert Hannigan, a former director of GCHQ, the British signals intelligence agency, told the Sunday Times: “We had a race to find out who he was his size, his hands, but, above all, his voice, made identifying him quite easy.”
One hurdle was recognising the voice in the video, which was released on August 19, 2014.
But GCHQ sound analysts worked their magic after they used technology to match the distorted voice with that of Emwazi whom security services had been tailing for three years after he fled the UK for Syria.
Veins on his hands were compared to an archive of photographs and found to be a match.
Jihadi John first emerged in August 2014, featuring in a series of sick videos released by the bloodthirsty extremist group.
He was part of four British jihadis who were nicknamed the Beatles.
In the clips he was filmed beheading various western hostages including two Britons, David Haines and Alan Henning.
Despite his efforts to remain invisible, such as using encryption programmes and wiping every computer he used to send messages, British intelligence detected him when he contacted his wife and child who lived in Iraq.
The maniac was then tracked down and killed by a US drone strike in November 2015 in Raqqa, in Syria.
He had been walking along a square, which was at the time the capital of the self-styled Caliphate, when a missile blew him to bits.
US Colonel Steve Warren said at the time: “I watched the video when we killed Jihadi John.
“We found him when he was alone on the street, when he was talking on the cell phone.
“And when it was all over, he was a greasy spot on the ground.”
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