The journalist claimed to have been murdered by Islamic State extremists was a freelancer Time and Foreign Policy magazines and had last been seen in Syria in August 2013.
He appeared in a video released online last month by the IS group that showed the beheading of fellow American journalist James Foley.
I've been told at the Nato summit that the intelligence services know exactly who 'Jihadi John' is - or at least are 99.9% certain.
The British aid worker being held by Islamic State is David Haines, a 44-year-old father-of-two from Perth, Scotland.
In a video statement which claims to record his final words US hostage and journalist Steven Sotloff blames US foreign policy for his death.