**EDITORS PLEASE NOTE: THIS EDIT CONTAINS GRAPHIC / REUTERS IS UNABLE TO INDEPENDENTLY VERIFY THE AUTHENTICITY OF THIS VIDEO**<br/> <br />Islamic State militants fighting in Iraq and Syria released video Saturday purportedly showing the beheading of British aid worker David Haines.<br/> <br />Reuters could not immediately verify the footage.<br/> <br />The images are consistent with that of the filmed executions of two American journalists, James Foley and Steven Sotloff.<br/> <br />British Prime Minister David Cameron said Saturday the murder was an act of pure evil and vowed to bring his killers to justice however long it takes.<br/> <br />Haines, a 44-year-old father of two from Perth in Scotland, was kidnapped last year while working for a French AID agency.
