In the wake of the African Embassy Bombings in 1998, President Clinton issued three top secret "Memoranda of Understanding," which authorized the CIA to kill Bin Laden and his key lieutenants--fewer than ten people overall--only if they resisted arrest. The CIA interpreted the memoranda as insufficient by limiting the use of lethal force. As George Tenet noted in his memoir, "Almost every authority granted to CIA prior to 9/11 made it clear that just going out and assassinating [Bin Laden] would not have been permissible or acceptable."

After 9/11, President George W. Bush made the policy of targeted killing more explicit. Just six days after the attacks, Bush signed a Memorandum of Notification that authorized the CIA to kill, without further presidential approval, some two dozen al-Qaeda leaders who appeared on an inital "high-value target list."

Included on this list was Abu Ali al-Harithi, an operational planner in the al-Qaeda cell that attacked the U.S.S. Cole. On November 3, 2002, a Predator drone killed al-Hariti, four Yemenis, and Ahmed Hijazi, a naturalized U.S. citizen and the ringleader of an alleged terrorist sleeper cell in Lackawanna, New York. This was the first targeted killing outside of Iraq and Afghanistan, and the first such killing of a naturalized U.S. citizen.

In Pakistan, the U.S. counterterrorism approach after 9/11 focused primarily on law enforcement and intelligence exploitation through arrest and interrogation (including torture) followed by either release or imprisonment. As the State Department's Patterns of Global Terrorism: 2002 report stated: "The Government of Pakistan arrested and transferred to US custody nearly 500 suspected al-Qaida and Taliban terrorists."

By 2004, however, the United States largely stopped detaining suspected operatives from Pakistan, and instead began killing them with armed Predator drones.

Initially, the intended targets were a limited number of well-known senior al-Qaeda and Taliban officials. Between 2004 and the end of 2007, there were only ten drone strikes in Pakistan. However, in mid-2008, President Bush authorized a vast expansion in the scope and intensity of the use of drones in Pakistan. Since then, there have been an additional 250 strikes. As David Sanger reported, Bush lowered the threshold for an attack to what one anonymous U.S. official described as the "reasonable man" standard: "If it seemed reasonable, you could hit it."

Now, nameless militants whose behavior--as determined by "pattern of life" surveillance--bears the "signature characteristics" of providing "operational support" to terrorist organizations can be targeted by drone strikes.

In Somalia, the United States backed the Ethiopian invasion and regime change effort that began in December 2006. On January 7, 2007, a U.S. Air Force Special Operations AC-130 gunship flying out of an airport in eastern Ethiopia fired on a convoy of escaping Islamic militants in southern Somalia. Since then, there have been an estimated six more attempted targeted killings there, including by AC-130s, U.S. Navy cruise missiles, special operations raids, and, as of this past June, armed drones.