When perpetrated against uniformed military, they are probably also a crime but under different provisos in international law. Individuals who engage in acts of warfare, but do not bear arms openly or wear a distinguishing uniform or emblem (like an armband) are francs tireurs and have the same protections under international law as spies: none.
What Rabbi Hier suggests though would make it much easier to track and make life difficult for the enablers of suicide bombers -- because, after all, you're not going to collect the pieces of the bomber in a basket and tell him he's under arrest....
d.o.l.
Criminal Number 18F