Argument: Assassinations are justified in self-defense, preventing imminent attack
David Kretzmer. "Targeted Killing of Suspected Terrorists: Extra-Judicial Executions or Legitimate Means of Defence?". European Journal of International Law. 2005 - "The author examines the legality of such killings under norms of international human rights law and international humanitarian law. Under the former system, such killings can only be lawful when carried out to prevent an imminent attack that cannot be stopped by other means."
Abraham D. Sofaer. "Responses to Terrorism. Targeted killing is a necessary option.". San Francisco Chronicle. March 26, 2004 - "Using force in international affairs is not merely risky, it is always controversial. Yet, targeted killing is sometimes necessary, because leaders are obliged to defend their citizens, just as police forces are obliged to defend communities. Leaders such as bin Laden or Yassin attempt to achieve their objectives through uses of force that are condemned by conventions subscribed to by all states. It is unlawful in all societies to kill people at random in order to secure any political objective, however sympathetic.
It is essential not to allow loaded rhetoric to obscure the propriety of lawfully using deadly force in self-defense. When people call a targeted killing an "assassination," they are attempting to preclude debate on the merits of the action. Assassination is widely defined as murder, and is for that reason prohibited in the United States by executive order. U.S. officials may not kill people merely because their policies are seen as detrimental to our interests, and properly so. But killings in self-defense are no more "assassinations" in international affairs than they are murders when undertaken by our police forces against domestic killers. Targeted killings in self-defense have been authoritatively determined by the federal government to fall outside the assassination prohibition.
International lawyers make all sorts of claims about the meaning of self- defense. Some are so averse to uses of force that they construe the U.N. Charter to allow self-defense only in response to "attacks" by the regular forces of a state within the territory of the state seeking to defend itself. The United States, under Democratic and Republican administrations alike, has repeatedly rejected such artificial limitations. The law is very clear, though, that an act of self-defense, especially a use of deadly force, must be necessary and must also be a proportionate measure in the light of the threat it is intended to address."