In the United States, the murder of Mr Sotloff was greeted with anger by the White House, and sympathy for his family.
President Obama is heading to Europe this week - where he'll discuss how to combat the threat of Islamic State, at the Nato summit in Cardiff.
But as ITV News correspondent Robert Moore reports from Washington, he will leave behind a mother whose appeal to save her son went unanswered:
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.