dismal said:
			
		
	
	
		
		
			I'll invoke Keith&Co's axiom that people who really want to kill someone with a bomb probably will conceal the fact they planted a bomb.
Thus these threats should probably just be ignored.
		
		
	 
The IRA would frequently plant a bomb, call in a threat to get the building evacuated, and then the bomb would go off, destroying the building.  Best not to ignore them.  
This confused me the first time I heard about it, but then I realized the goal was not to kill people, but to break their spirits.  By calling in the threat, everyone who was saved must go through their lives knowing that they owe it to the mercy of the terrorists.  And if the authorities ignore the warnings and the bomb kills many, the strife caused will be most effective.  
People have this simplistic notion that war is about killing your enemies.  This is not correct.