A film purporting to show the beheading of James Foley was probably staged, according to a forensic science company, which suggests the American journalist's execution may have been carried out off-camera.

A blip in the footage, released on social media last week by Islamic State militants, indicated that Foley may have had to repeat a line as he read a script to camera while kneeling in the sand with his hands tied.

James Foley: May have been killed after the camera stopped. Credit:AP

The footage was most likely edited later using "slick post-production techniques", according to the analysis for The Times in London by an unnamed international forensic science company that has worked for police forces across Britain, the news organisation claimed.