On this point there is resounding agreement among our experts: Any response must adhere to the Geneva Conventions, the Hague Regulations, and all the other laws and customs of war. The most fundamental rule is that civilians and civilian buildings are immune from military attack and must not be targeted. Belligerents must at all times distinguish between military and civilian sites and direct their attacks only against the former. Military necessity must be balanced against the principle of “proportionality,” which dictates that all precautions be taken to minimize “collateral damage” (i.e., civilian casualties). “You cannot fight terror with terror,” one of our experts emphasized.

The difficulty in this case is that terrorists by definition do not wear uniforms, and deliberately protect themselves by blending in with the civilian population. All our experts are concerned that, in this scenario, the risk of collateral damage is high.