There's a general tendency to treat large-scale violence and force in bureaucratic language. Nobody would call a bunch of thugs who ride into a village and murd

There's a general tendency to treat large-scale violence and force in bureaucratic language. Nobody would call a bunch of thugs who ride into a village and murder all the people they don't like something other than a bunch of murderers. But once they claim authority and do it in large numbers or in a somewhat legitimized ("legitimization by procedure") way, those murders are being called 'executions' like in the area under control of the IS.