In London in 2011, the police withdrew protection from property while dealing with a riot.  Within an hour, looters were burning people out of their homes and within a day a man was beaten to death.  Same happened in Dublin, Ireland in 1916 and in Baghdad, Iraq in 2003. 

Take away the man with the gun and people immediately start looting and soon will start killing.  The man with the gun is exactly why they don't loot, pillage and kill.