Anger and defiance from david ka cameron. Its showing the execution of a british aid worker. The third westerner beheaded in recent weeks by the Islamic Militant group. Heres David Cameron today. They are killing and slaughtering thousands of people. Muslims, christians, minorities across iraq and syria. They boast of their brutality. They claim to do this in the name of islam that is nonsense. Islam is a religion of peace. They are not muslims, they are monsters. We have reaction today from the white house and Nbcs Kristen Welker. But first, lets head to london and get the latest there. Cassandra with a welcome, what have you learned about this new isis propaganda video . And what is the reaction there in britain . The video is released last night showing the execution of david haines an aid worker taken in syria. And isis militants threatened the life of another uk hostage. Its been received here with disgust, people are sick, and also the uk is grieving the loss of an aid worker who