Group releases video showing murder of David Haines, weeks after killing US hostages James Foley and Steven Sotloff. Al Jazeera's Sue Turton reports from northern Iraq. Subscribe to our channel http://bit.ly/AJSubscribe Follow us on Twitter https://twitter.com/AJEnglish Find us on Facebook https://www.facebook.com/aljazeera Check our website: http://www.aljazeera.com/