New Delhi, Sep 14 (ANI): Islamic State militants fighting in Iraq and Syria released video purportedly showing the beheading of British aid worker David Haines. The images are consistent with that of the filmed executions of two American journalists, James Foley and Steven Sotloff. British Prime Minister David Cameron said the murder was an act of pure evil and vowed to bring his killers to justice however long it takes. Haines, a 44-year-old from Perth in Scotland, was kidnapped last year while working for a French AID agency.