Islamic State Kassig murder: Western jihadists probed 17 November 2014 Last updated at 19:37 Western intelligence officials are trying to identify Islamic State (IS) militants seen in the video that shows the beheading of US aid worker Abdul-Rahman Kassig and 18 Syrian prisoners. A third militant was reported to be a Briton, although the father of Nasser Muthana, 20, now denies it is his son. But Mr Muthana now says his son is not among the jihadists in the video. Abdul-Rahman Kassig is being mourned "as a fallen hero" by Syria's opposition, the BBC's Frank Gardner reports Legacy pledge The IS video shows a masked man standing over a severed head, which the White House confirmed was Mr Kassig's. His parents, Ed and Paula, from Indiana, said in a statement they were heartbroken by his death. Paris prosecutor Francois Molins identified Maxime Hauchard as appearing in the video. Hauchard told French TV station BFM via Skype in July that he was in Raqqa in Syria and had joined IS, adding: "The personal objective of everyone here is shahid (martyrdom). That is the greatest reward. Hauchard's uncle told French TV on Monday: "I can't believe it was he who cut anyone's head off. It's not possible. He wouldn't hurt a fly. He was a calm and happy little boy. Mr Molins said another Frenchman could be among the militants but that it had not yet been confirmed. Jihadi John In Britain, Muthana's father, Ahmed, initially said it was his son, but then said the images were blurry and he was not sure. He now says that although he has not seen the footage, he is able to confirm it is not his son from images he has seen. Mr Muthana told the BBC: "It doesn't look like him, much difference. This one's got a big nose, my one has a flat nose. Nasser Muthana appeared in an IS video in June that was aimed at recruitment. This man is dressed in black with a balaclava, while the rest of the militants wear army fatigues. "Jihadi John" has been shown in previous IS videos of the beheadings of the other Western hostages: Britons Alan Henning and David Haines, and US journalists James Foley and Steven Sotloff.