Miller writes: "Targeted killing... is not 'assassination.'" Associate Professor Eric Patterson and Teresa Casale wrote, "Perhaps most important is the legal distinction between targeted killing and assassination." On the other hand, the American Civil Liberties Union also states on its website, "A program of targeted killing far from any battlefield, without charge or trial, violates the constitutional guarantee of due process. It also violates international law, under which lethal force may be used outside armed conflict zones only as a last resort to prevent imminent threats, when non-lethal means are not available. Targeting people who are suspected of terrorism for execution, far from any war zone, turns the whole world into a battlefield." Yael Stein, the research director of B'Tselem, the Israeli Information Center for Human Rights in the Occupied Territories, also stated in her article "By Any Name Illegal and Immoral: Response to 'Israel's Policy of Targeted Killing'": The argument that this policy affords the public a sense of revenge and retribution could serve to justify acts both illegal and immoral. Clearly, lawbreakers ought to be punished. Yet, no matter how horrific their deeds, as the targeting of Israeli civilians indeed is, they should be punished according to the law. David's arguments could, in principle, justify the abolition of formal legal systems altogether. Targeted killing has become a frequent tactic of the United States and Israel in their fight against terrorism. The tactic can raise complex questions and lead to contentious disputes as to the legal basis for its application, who qualifies as an appropriate "hit list" target, and what circumstances must exist before the tactic may be used. Opinions range from people considering it a legal form of self-defense that decreases terrorism to people calling it an extrajudicial killing that lacks due process and leads to further violence. Methods used have included firing Hellfire missiles from Predator or Reaper drones (unmanned, remote-controlled planes), detonating a cell phone bomb, and long-range sniper shooting. Countries such as the US (in Pakistan and Yemen) and Israel (in the West Bank and Gaza) have used targeted killing to eliminate members of groups such as Al-Qaeda and Hamas. In early 2010, with President Obama's approval, Anwar al-Awlaki became the first US citizen to be publicly approved for targeted killing by the Central Intelligence Agency. Awlaki was killed in a drone strike in September 2011. United Nations investigator Ben Emmerson said that US drone