On August 5th, officials at the Central Intelligence Agency, in Langley, Virginia, watched a live video feed relaying closeup footage of one of the most wanted terrorists in Pakistan. Baitullah Mehsud, the leader of the Taliban in Pakistan, could be seen reclining on the rooftop of his father-in-law's house, in Zanghara, a hamlet in South Waziristan.

It was a hot summer night, and he was joined outside by his wife and his uncle, a medic; at one point, the remarkably crisp images showed that Mehsud, who suffered from diabetes and a kidney ailment, was receiving an intravenous drip.

The video was being captured by the infrared camera of a Predator drone, a remotely controlled, unmanned plane that had been hovering, undetected, two miles or so above the house. Pakistan's Interior Minister, A. Rehman Malik, told me recently that Mehsud was resting on his back. Malik, using his hands to make a picture frame, explained that the Predator's targeters could see Mehsud's entire body, not just the top of his head. "It was a perfect picture," Malik, who watched the videotape later, said. "We used to see James Bond movies where he talked into his shoe or his watch. We thought it was a fairy tale. But this was fact!" The image remained just as stable when the C.I.A. remotely launched two Hellfire missiles from the Predator. Authorities watched the fiery blast in real time. After the dust cloud dissipated, all that remained of Mehsud was a detached torso. Eleven others died: his wife, his father-in-law, his mother-in-law, a lieutenant, and seven bodyguards.

Pakistan's government considered Mehsud its top enemy, holding him responsible for the vast majority of recent terrorist attacks inside me country, including the assassination of former Prime Minister Benazir Bhutto, in December, 2007, and the bombing, last September, of the Marriott Hotel in Islamabad, which killed more man fifty people. Mehsud was also thought to have helped his Afghan confederates attack American and coalition troops across the border. Roger Cressey, a former counterterrorism official on the National Security Council who is now a partner at Good Harbor, a consulting firm, told me, "Mehsud was someone both we and Pakistan were happy to see go up in smoke." Indeed, there was no controversy when, a few days after the missile strike, CNN reported that President Barack Obama had authorized it.

However, at about the same time, there was widespread anger after the Wall Street Journal revealed that during the Bush Administration the C.I.A. had considered setting up hit squads to capture or kill Al Qaeda operatives around the world.

The furor grew when the Times reported that the C.I.A. had turned to a private contractor to help with this highly sensitive operation: the controversial firm Blackwater, now known as Xe Services. Members of the Senate and House intelligence committees demanded investigations of the program, which, they said, had been hidden from them. And many legal experts argued that, had the program become fully operational, it would have violated a 1976 executive order, signed by President Gerald R Ford, banning American intelligence forces from engaging in assassination.

Hina Shamsi, a human-rights lawyer at the New York University School of Law, was struck by the inconsistency of the public's responses. "We got so upset about a targeted-killing program that didn't happen," she told me. "But the drone program exists." She said of the Predator program, "These are targeted international killings by the state." The program, as it happens, also uses private contractors for a variety of tasks, including flying the drones. Employees of Xe Services maintain and load the Hellfire missiles on the aircraft. Vicki Divoll, a former C.I.A. lawyer, who now teaches at the U.S. Naval Academy, in Annapolis, observed, "People are a lot more comfortable with a Predator strike that kills many people than with a throat-slitting that kills one." But, she added, "mechanized killing is still killing."

The U.S. government runs two drone programs. The military's version, which is publicly acknowledged, operates in the recognized war zones of Afghanistan and Iraq, and targets enemies of US. troops stationed there. As such, it is an extension of conventional warfare. The C.I.A.'s program is aimed at terror suspects around the world, including in countries where U.S. troops are not based. It was initiated by the Bush Administration and, according to Juan Zarate, a counterterrorism adviser in the Bush White House, Obama has left in place virtually all the key personnel. The program is classified as covert, and the intelligence agency declines to provide any information to the public about where it operates, how it selects targets, who is in charge, or how many people have been killed.

Nevertheless, reports of fatal air strikes in Pakistan emerge every few days. Such stories are often secondhand and difficult to confirm, as the Pakistani government and the military have tried to wall off the tribal areas from journalists. But, even if a precise account is elusive, the outlines are clear: the C.I.A. has joined the Pakistani intelligence service in an aggressive campaign to eradicate local and foreign militants, who have taken refuge in some of the most inaccessible parts of the country.

The first two C.I.A. air strikes of the Obama Administration took place on the morning of January 23rd -- the President's third day in office. Within hours, it was clear that the morning's bombings, in Pakistan, had killed an estimated twenty people. In one strike, four Arabs, all likely affiliated with Al Qaeda, died. But in the second strike a drone targeted the wrong house, hitting the residence of a pro-government tribal leader six miles outside the town of Wana, in South Waziristan. The blast killed the tribal leader's entire family, including three children, one of them five years old. In keeping with US. policy, there was no official acknowledgment of either strike.

Since then, the C.I.A. bombardments have continued at a rapid pace. According to a just completed study by the New America Foundation, the number of drone strikes has risen dramatically since Obama became President. During his first nine and a half months in office, he has authorized as many C.I.A. aerial attacks in Pakistan as George W. Bush did in his final three years in office. The study's authors, Peter Bergen and Katherine Tiedemann, report that the Obama Administration has sanctioned at least forty'-one C.I.A. missile strikes in Pakistan since taking office -- a rate of approximately one bombing a week. So far this year, various estimates suggest, the C.I.A. attacks have killed between three hundred and twenty-six and five hundred and thirty-eight people. Critics say that many of the victims have been innocent bystanders, including children.

In the last week of September alone, there were reportedly four such attacks -- three of them in one twenty-four-hour period. At any given moment, a former White House counterterrorism official says, the C.I.A. has multiple drones flying over Pakistan, scouting for targets. According to the official, "there are so many drones" in the air that arguments have erupted over which remote operators can claim which targets, provoking "command-and-control issues." General Atomics Aeronautical Systems, the defense contractor that manufactures the Predator and its more heavily armed sibling, the Reaper, can barely keep up with the government's demand. The Air Force's fleet has grown from some fifty drones in 2001 to nearly two hundred; the C.I.A. will not divulge how many drones it operates. The government plans to commission hundreds more, including new generations of tiny "nano" drones, which can fly after their prey like a killer bee through an open window.

With public disenchantment mounting over the U.S. troop deployment in Afghanistan, and the Obama Administration divided over whether to escalate the American military presence there, many in Washington support an even greater reliance on Predator strikes. In this view, the U.S., rather than trying to stabilize Afghanistan by waging a counter-insurgency operation against Taliban forces, should focus purely on counterterrorism, and use the latest technology to surgically eliminate Al Qaeda leaders and their allies. In September, the conservative pundit George Will published an influential column in the Washington Post, "Time to Get Out of Afghanistan," arguing that "America should do only what can be done from offshore, using intelligence, drones, cruise missiles, air strikes and small, potent Special Forces units, concentrating on the porous 1,500-mile border with Pakistan, a nation that actually matters." Vice-President Joseph Biden reportedly holds a similar view.

It's easy to understand the appeal of a "push-button" approach to fighting Al Qaeda, but the embrace of the Predator program has occurred with remarkably little public discussion, given that it represents a radically new and geographically unbounded use of state-sanctioned lethal force. And, because of the C.I.A. program's secrecy, there is no visible system of accountability in place, despite the fact that the agency has killed many civilians inside a politically fragile, nuclear-armed country with which the U.S. is not at war.

Should something go wrong in the C.I.A.'s program -- last month, the Air Force lost control of a drone and had to shoot it down over Afghanistan -- it's unclear what the consequences would be. The Predators in the C.I.A. program are "flown" by civilians, both intelligence officers and private contractors. According to a former counterterrorism official, the contractors are "seasoned professionals -- often retired military and intelligence officials." (The intelligence agency outsources a significant portion of its work.) Within the C.I.A., control of the unmanned vehicles is split among several teams. One set of pilots and operators works abroad, near hidden airfields in Afghanistan and Pakistan, handling takeoffs and landings. Once the drones are aloft, the former counterterrorism official said, the controls are electronically "slewed over" to a set of "reachback operators," in Langley. Using joysticks that resemble video-game controllers, the reachback operators -- who don't need conventional flight training -- sit next to intelligence officers and watch, on large flat-screen monitors, a live video feed from the drone's camera.

From their suburban redoubt, they can turn the plane, zoom in on the landscape below, and decide whether to lock onto a target. A stream of additional "signal" intelligence, sent to Langley by the National Security Administration [sic, Agency], provides electronic means of corroborating that a target has been correctly identified. The White House has delegated trigger authority to C.I.A. officials, including the head of the Counter-Terrorist Center, whose identity remains veiled from the public because the agency has placed him under cover.

People who have seen an air strike live on a monitor described it as both awe-inspiring and horrifying. "You could see these little figures scurrying, and the explosion going off, and when the smoke cleared there was just rubble and charred stuff," a former C.LA. officer who was based in Afghanistan after September 11th says of one attack. (He watched the carnage on a small monitor in the field.) Human beings running for cover are such a common sight that they have inspired a slang term: "squirters." Peter W. Singer, the author of "Wired for War," a recent book about the robotics revolution in modern combat, argues that the drone technology is worryingly "seductive," because it creates the perception that war can be "costless." Cut off from the realities of the bombings in Pakistan, Americans have been insulated from the human toll, as well as from the political and the moral consequences.

Nearly all the victims have remained faceless, and the damage caused by the bombings has remained unseen. In contrast to Gaza, where the targeted killing of Hamas fighters by the Israeli military has been extensively documented -- making clear that the collateral damage, and the loss of civilian life, can be severe -- Pakistan's tribal areas have become largely forbidden territory for media organizations. As a result, no videos of a drone attack in progress have been released, and only a few photographs of the immediate aftermath of a Predator strike have been published.

The seeming unreality of the Predator enterprise is also felt by the pilots. Some of them reportedly wear flight suits when they operate a drone's remote controls. When their shifts end, of course, these cubicle warriors can drive home to have dinner with their families. Critics have suggested that unmanned systems, by sparing these combatants from danger and sacrifice, are creating what Sir Brian Burridge, a former British Air Chief Marshal in Iraq, has called "a virtueless war," requiring neither courage nor heroism. According to Singer, some Predator pilots suffer from combat stress that equals, or exceeds, that of pilots in the battlefield. This suggests that virtual killing, for all its sterile trappings, is a discomfiting form of warfare. Meanwhile, some social critics, such as Mary Dudziak, a professor at the University of Southern California's Gould School of Law, argue that the Predator strategy has a larger political cost. As she puts it, "Drones are a technological step that further isolates the American people from military action, undermining political checks on . . . endless war."

The advent of the Predator targeted killing program "is really a sea change," says Gary Solis, who teaches at Georgetown University's Law Center and recently retired from running the law program at the U.S. Military Academy. "Not only would we have expressed abhorrence of such a policy a few years ago; we did." In July, 2001, two months before Al Qaeda's attacks on New York and Washington profoundly altered America's mindset, the U.S. denounced Israel's use of targeted killing against Palestinian terrorists. The American Ambassador to Israel, Martin Indyk, said at the time, "The United States government is very clearly on record as against targeted assassinations.  . . . They are extrajudicial killings, and we do not support that."

Before September 11th, the C.I.A., which had been chastened by past assassination scandals, refused to deploy the Predator for anything other than surveillance. Daniel Benjamin, the State Department's counterterrorism director, and Steven Simon, a former counterterrorism adviser, report in their 2002 book "The Age of Sacred Terror" that the week before Al Qaeda attacked the U.S. George Tenet, then the agency's director, argued that it would be "a terrible mistake" for "the Director of Central Intelligence to fire a weapon like this."

Yet once America had suffered terrorist attacks on its own soil the agency's posture changed, and it petitioned the White House for new authority. Within days, President Bush had signed a secret Memorandum of Notification, giving the C.I.A. the right to kill members of Al Qaeda and their confederates virtually anywhere in the world. Congress endorsed this policy, passing a bill called the Authorization for Use of Military Force. Bush's legal advisers modelled their rationale on Israel's position against terrorism, arguing that the U.S. government had the right to use lethal force against suspected terrorists in "anticipatory" self-defense. By classifying terrorism as an act of war, rather than as a crime, the Bush Administration reasoned that it was no longer bound by legal constraints requiring the government to give suspected terrorists due process.

In November, 2002, top Bush Administration officials publicly announced a successful Predator strike against an Al Qaeda target, Qaed Salim Sinan al-Harethi, a suspect in the 2000 bombing of the U.S.S. Cole. Harethi was killed after a Hellfire missile vaporized the car in which he and five other passengers were riding, on a desert road in Yemen.

Paul Wolfowitz, then the Deputy Defense Secretary, praised the new tactic, telling CNN, "One hopes each time that you get a success like that, not only to have gotten rid of somebody dangerous but to have imposed changes in their tactics, operations, and procedures." At first, some intelligence experts were uneasy about drone attacks. In 2002, Jeffrey Smith, a former C.I.A. general counsel, told Seymour M. Hersh, for an article in this magazine, "If they're dead, they're not talking to you, and you create more martyrs." And, in an interview with the Washington Post, Smith said that ongoing drone attacks could "suggest that it's acceptable behavior to assassinate people.  . . . Assassination as a norm of international conduct exposes American leaders and Americans overseas." Seven years later, there is no longer any doubt that targeted killing has become official U.S. policy. "The things we were complaining about from Israel a few years ago we now embrace," Solis says. Now, he notes, nobody in the government calls it assassination.

The Predator program is described by many in the intelligence world as America's single most effective weapon against Al Qaeda. In May, Leon Panetta, the C.LA.'s director, referred to the Predator program as "the only game in town" in an unguarded moment after a public lecture. Counterterrorism officials credit drones with having killed more than a dozen senior Al Qaeda leaders and their allies in the past year, eliminating more than half of the C.I.A.'s twenty most wanted "high value" targets. In addition to Baitullah Mehsud, the list includes Nazimuddin Zalalov, a former lieutenant of Osama bin Laden; Ilyas Kashmiri, Al Qaeda's chief of paramilitary operations in Pakistan; Saad bin Laden, Osama's eldest son; Abu Sulayman al-Jazairi, an Algerian Al Qaeda planner who is believed to have helped train operatives for attacks in Europe and the United States; and Osama al-Kini and Sheikh Ahmed Salim Swedan, Al Qaeda operatives who are thought to have played central roles in the 1998 bombings of American embassies in East Africa.

Juan Zarate, the Bush counterterrorism adviser, believes that "Al Qaeda is on its heels" partly because "so many bigwigs" have been killed by drones. Though he acknowledges that Osama bin Laden and Ayman al-Zawahiri, the group's top leaders, remain at large, he estimates that no more than fifty members of Al Qaeda's senior leadership still exist, along with two to three hundred senior members outside the terror organization's "inner core." Zarate and other supporters of the Predator program argue that it has had positive ripple effects. Surviving militants are forced to operate far more cautiously, which diverts their energy from planning new attacks. And there is evidence that the drone strikes, which depend on local informants for targeting information, have caused debilitating suspicion and discord within the ranks. Four Europeans who were captured last December after trying to join Al Qaeda in Pakistan described a life of constant fear and distrust among the militants, whose obsession with drone strikes had led them to communicate only with elaborate secrecy and to leave their squalid hideouts only at night. As the Times has reported, militants have been so unnerved by the drone program that they have released a video showing the execution of accused informants. Pakistanis have also been gripped by rumors that paid C.I.A. informants have been planting tiny silicon-chip homing devices for the drones in the tribal areas.

The drone program, for all its tactical successes, has stirred deep ethical concerns. Michael Walzer, a political philosopher and the author of the book "Just and Unjust Wars," says that he is unsettled by the notion of an intelligence agency wielding such lethal power in secret. "Under what code does the C.I.A. operate?" he asks. "I don't know. The military operates under a legal code, and it has judicial mechanisms." He said of the C.I.A.'s drone program, "There should be a limited, finite group of people who are targets, and that list should be publicly defensible and available. Instead, it's not being publicly defended. People are being killed, and we generally require some public justification when we go about killing people."

Since 2004, Philip Alston, an Australian human-rights lawyer who has served as the United Nations Special Rapporteur on Extrajudicial, Summary, or Arbitrary Executions, has repeatedly tried, but failed, to get a response to basic questions about the C.I.A.'s program-first from the Bush Administration, and now from Obama's. When he asked, in formal correspondence, for the C.I.A's legal justifications for targeted killings, he says, "they blew me off" (A C.I.A spokesperson told me that the agency "uses lawful, highly accurate, and effective tools and tactics to take the fight to Al Qaeda and its violent allies. That careful, precise approach has brought major success against a very dangerous and deadly enemy.") Alston then presented a critical report on the drone program to the U.N. Human Rights Council, but, he says, the U.S. representatives ignored his concerns.

Alston describes the C.I.A. program as operating in "an accountability void," adding, "It's a lot like the torture issue. You start by saying , we'll just go after the handful of 9/11 masterminds. But, once you've put the regimen for waterboarding and other techniques in place, you use it much more indiscriminately. It becomes standard operating procedure. It becomes all too easy. Planners start saying, 'Let's use drones in a broader context.' Once you use targeting less stringently, it can become indiscriminate."

Under international law, in order for the U.S. government to legally target civilian terror suspects abroad it has to define a terrorist group as one engaging in armed conflict, and the use of force must be a "military necessity." There must be no reasonable alternative to killing, such as capture, and to warrant death the target must be "directly participating in hostilities." The use of force has to be considered "proportionate" to the threat. Finally, the foreign nation in which such targeted killing takes place has to give its permission.

Many lawyers who have looked at America's drone program in Pakistan believe that it meets these basic legal tests. But they are nevertheless troubled, as the U.S. government keeps broadening the definition of acceptable high-value targets. Last March, the Obama Administration made an unannounced decision to win support for the drone program inside Pakistan by giving President Asif Ali Zardari more control over whom to target. "A lot of the targets are nominated by the Pakistanis -- it's part of the bargain of getting Pakistani cooperation," says Bruce Riedel, a former C.I.A. officer who has served as an adviser to the Obama Administration on Afghanistan and Pakistan. According to the New America Foundation's study, only six of the forty-one C.I.A. drone strikes conducted by the Obama Administration in Pakistan have targeted Al Qaeda members. Eighteen were directed at Taliban targets in Pakistan, and fifteen were aimed specifically at Baitullah Mehsud. Talat Masood, a retired Pakistani lieutenant general and an authority on security issues, says that the U.S.'s tactical shift, along with the elimination of Mehsud, has quieted some of the Pakistani criticism of the American air strikes, although the bombings are still seen as undercutting the country's sovereignty. But, given that many of the targeted Pakistani Taliban figures were obscure in U.S. counterterrorism circles, some critics have wondered whether they were legitimate targets for a Predator strike. "These strikes are killing a lot of low-level militants, which raises the question of whether they are going beyond the authorization to kill leaders," Peter Bergen told me. Roger Cressey, the former National Security Council official, who remains a strong supporter of the drone program, says, "The debate is that we've been doing this so long we're now bombing low-level guys who don't deserve a Hellfire missile up their ass." (In his view, "Not every target has to be a rock star.")

The Obama Administration has also widened the scope of authorized drone attacks in Afghanistan. An August report by the Senate Foreign Relations Committee disclosed that the Joint Integrated Prioritized Target List -- the Pentagon's roster of approved terrorist targets, containing three hundred and sixty-seven names -- was recently expanded to include some fifty AFghan drug lords who are suspected of giving money to help finance the Taliban. These new targets are a step removed from Al Qaeda. According to the Senate report, "There is no evidence that any significant amount of the drug proceeds goes to Al Qaeda." The inclusion of Afghan narcotics traffickers on the U.S. target list could prove awkward, some observers say, given that President Hamid Karzai's running mate, Marshal Mohammad Qasim Fahim, and the President's brother, Ahmed Wali Karzai, are strongly suspected of involvement in narcotics. Andrew Bacevich, a professor of history and international relations at Boston University, who has written extensively on military matters, said, "Are they going to target Karzai's brother?" He went on, 'We should be very careful about who we define as the enemy we have to kill. Leaders of Al Qaeda, of course. But you can't kill people on Tuesday and negotiate with them on Wednesday."

Defining who is and who is not too tangential for the U.S. to kill can be difficult. John Radsan, a former lawyer in the C.I.A's office of general counsel, who is now a professor at William Mitchell College of Law, in St. Paul, Minnesota, says, "You can't target someone just because he visited an Al Qaeda Web site. But you also don't want to wait until they're about to detonate a bomb. It's a sliding scale." Equally fraught is the question of how many civilian deaths can be justified. "If it's Osama bin Laden in a house with a four-year-old, most people will say go ahead," Radsan says. "But if it's three or four children? Some say that's too many. And if he's in a school? Many say don't do it." Such judgment calls are being made daily by the C.I.A., which, Radsan points out, "doesn't have much experience with killing. Traditionally, the agency that does that is the Department of Defense."

Though the C.I.A:s methodology remains unknown, the Pentagon has created elaborate formulas to help the military make such lethal calculations. A top military expert, who declined to be named, spoke of the military's system, saying, "There's a whole taxonomy of targets." Some people are approved for killing on sight. For others, additional permission is needed. A target's location enters the equation, too. If a school, hospital, or mosque is within the likely blast radius of a missile, that, too, is weighed by a computer algorithm before a lethal strike is authorized. According to the recent Senate Foreign Relations Committee report, the U.S. military places no name on its targeting list until there are "two verifiable human sources" and "substantial additional evidence" that the person is an enemy.

In Israel, which conducts unmanned air strikes in the Palestinian territories, the process of identifying targets, in theory at least, is even more exacting. Military lawyers have to be convinced that the target can't reasonably be captured, and that he poses a threat to national security. Military specialists in Arab culture also have to be convinced that the hit will do more good than harm. "You have to be incredibly cautious," Amos Guiora, a law professor at the University of Utah, says. From 1994 to 1997, he advised Israeli commanders on targeted killings in the Gaza Strip. "Not everyone is at the level appropriate for targeted killing," he says. "You want a leader, the hub with many spokes." Guiora, who follows the Predator program closely, fears that national security officials here lack a clear policy and a firm definition of success. "Once you start targeted killing, you better make damn sure there's a policy guiding it," he says. "It can't be just catch-as-catch-can."

Daniel Byman, the director of Georgetown University's Center for Peace and Security Studies, argues that, when possible, "it's almost always better to arrest terrorists than to kill them. You get intelligence then. Dead men tell no tales." The C.I.A.'s killing of.Saad bin Laden, Osama's son, provides a case in point. By the time that Saad bin Laden had reached Pakistan's tribal areas, late last year, there was little chance that any law-enforcement authority could capture him alive. But, according to Hillary Mann Leverett, an adviser to the National Security Council between 2001 and 2003, the Bush Administration would have had several opportunities to interrogate Saad bin Laden earlier, if it had been willing to make a deal with Iran, where, according to U.S. intelligence, he lived occasionally after September 11th. "The Iranians offered to work out an international framework for transferring terror suspects, but the Bush Administration refused," she said. In December, 2008, Saad bin Laden left Iran for Pakistan; within months, according to NPR., a Predator missile had ended his life. "We absolutely did not get the most we could," Leverett said. "Saad bin Laden would have been very, very valuable in terms of what he knew. He probably would have been a gold mine."

Byman is working on a book about Israel's experiences with counterterrorism, including targeted killing. Though the strikes there have weakened the Palestinian leadership, he said, "if you use these tools wrong, you can lose the moral high ground, which is going to hurt you. Inevitably, some of the intelligence is going to be wrong, so you're always rolling the dice. That's the reality of realtime intelligence."

Indeed, the history of targeted killing is marked by errors. In 1973, for example, Israeli intelligence agents murdered a Moroccan waiter by mistake. They thought that he was a terrorist who had been involved in slaughtering Israeli athletes at the Munich Olympics, a year earlier. And in 1986 the Reagan Administration attempted to retaliate against the Libyan leader Muammar Qaddafi for his suspected role in the deadly bombing of a disco frequented by American servicemen in Germany. The U.S. launched an air strike on Qaddafi's household. The bombs missed him, but they did kill his fifteen-month-old daughter.

The C.I.A.'s early attempts at targeting Osama bin Laden were also problematic. After Al Qaeda blew up the U.S. Embassies in Tanzania and Kenya, in August, 1998, President Bill Clinton retaliated, by launching seventy-five Tomahawk cruise missiles at a site in Afghanistan where bin Laden was expected to attend a summit meeting. According to reports, the bombardment killed some twenty Pakistani militants but missed bin Laden, who had left the scene hours earlier.

The development of the Predator, in the early nineteen-nineties, was supposed to help eliminate such mistakes. The drones can hover above a target for up to forty hours before refuelling, and the precise video footage makes it much easier to identify targets. But the strikes are only as accurate as the intelligence that goes into them. Tips from informants on the ground are subject to error, as is the interpretation of video images. Not long before September 11, 2001, for instance, several U.S. counterterrorism officials became certain that a drone had captured footage of bin Laden in a locale he was known to frequent in Afghanistan. The video showed a tall man in robes, surrounded by armed bodyguards in a diamond formation. At that point, drones were unarmed, and were used only for surveillance. "The optics were not great, but it was him," Henry Crumpton, then the C.I.A's top covert-operations officer for the region, told Time. But two other former C.I.A officers, who also saw the footage, have doubts. "It's like an urban legend," one of them told me. "They just jumped to conclusions. You couldn't see his face. It could have been Joe Schmo. Believe me, no tall man with a beard is safe anywhere in Southwest Asia." In February, 2002, along the mountainous eastern border of Afghanistan, a Predator reportedly followed and killed three suspicious Afghans, including a tall man in robes who was thought to be bin Laden.

The victims turned out to be innocent villagers, gathering scrap metal. In Afghanistan and Pakistan, the local informants, who also serve as confirming witnesses for the air strikes, are notoriously unreliable. A former C.I.A. officer who was based in Afghanistan after September 11th told me that an Afghan source had once sworn to him that one of Al Qaeda's top leaders was being treated in a nearby clinic. The former officer said that he could barely hold off an air strike after he passed on the tip to his superiors.

"They scrambled together an elite team," he recalled "We caught hell from headquarters. They said 'Why aren't you moving on it?' when we insisted on checking it out first." It turned out to be an intentionally false lead. "Sometimes you're dealing with tribal chiefs," the former officer said. "Often, they say an enemy of theirs is Al Qaeda because they just want to get rid of somebody. Or they made crap up because they wanted to prove they were valuable, so that they could make money. You couldn't take their word." The consequences of bad ground intelligence can be tragic. In September, a NATO air strike in Afghanistan killed between seventy and a hundred and twenty-five people, many of them civilians, who were taking fuel from two stranded oil trucks; they had been mistaken for Taliban insurgents. (The incident is being investigated by NATO.) According to a reporter for the Guardian, the bomb strike, by an F -15E fighter plane, left such a tangle of body parts that village elders resorted to handing out pieces of unidentifiable corpses to the grieving families, so that they could have something to bury. One Afghan villager told the newspaper, "1 took a piece of flesh with me home and I called it my son."

Predator drones, with their superior surveillance abilities, have a better track record for accuracy than fighter jets, according to intelligence officials. Also, the drone's smaller Hellfire missiles are said to cause far less collateral damage. Still, the recent campaign to kill Baitullah Mehsud offers a sobering case study of the hazards of robotic warfare. It appears to have taken sixteen missile strikes, and fourteen months, before the C.I.A. succeeded in killing him. During this hunt, between two hundred and seven and three hundred and twenty-one additional people were killed, depending on which news accounts you rely upon. It's all but impossible to get a complete picture of whom the C.I.A. killed during this campaign, which took place largely in Waziristan. Not only has the Pakistani government closed off the region to the outside press; it has also shut out international humanitarian organizations like the International Committee for the Red Cross and Doctors Without Borders. "We can't get within a hundred kilometres of Waziristan," Brice de la Vingne, the operational coordinator for Doctors Without Borders in Pakistan, told me. "We tried to set up an emergency room, but the authorities wouldn't give us authorization."

A few Pakistani and international news stories, most of which rely on secondhand sources rather than on eyewitness accounts, offer the basic details. On June 14, 2008, a C.I.A. drone strike on Mehsud's home town, Makeen, killed an unidentified person. On January 2,2009, four more unidentified people were killed. On February 14th, more than thirty people were killed, twenty-five of whom were apparently members of Al Qaeda and the Taliban, though none were identified as major leaders. On April 1st, a drone attack on Mehsud's deputy, Hakimullah Mehsud, killed ten to twelve of his followers instead. On April 29th, missiles fired from drones killed between six and ten more people, one of whom was believed to be an Al Qaeda leader. On May 9th, five to ten more unidentified people were killed; on May 12th, as many as eight people died. On June 14th, three to eight more people were killed by drone attacks. On June 23rd, the C.I.A. reportedly killed between two and six unidentified militants outside Makeen, and then killed dozens more people -- possibly as many as eighty-six -- during funeral prayers for the earlier casualties. An account in the Pakistani publication The News described ten of the dead as children. Four were identified as elderly tribal leaders. One eyewitness, who lost his right leg during the bombing, told Agence France-Presse that the mourners suspected what was coming: "After the prayers ended, people were asking each other to leave the area, as drones were hovering." The drones, which make a buzzing noise, are nicknamed machay (wasps) by the Pashtun natives, and can sometimes be seen and heard, depending on weather conditions. Before the mourners could clear out, the eyewitness said, two drones started firing into the crowd. "It created havoc," he said. "There was smoke and dust everywhere. Injured people were crying and asking for help." Then a third missile hit. "I fell to the ground," he said.

The local population was clearly angered by the Pakistani government for allowing the U.S. to target a funeral. (Intelligence had suggested that Mehsud would be among the mourners.) An editorial in The News denounced the strike as sinking to the level of the terrorists. The Urdu newspaper Jang declared that Obama was "shutting his ears to the screams of thousands of women whom your drones have turned into dust." U.S. officials were undeterred, continuing drone strikes in the region until Mehsud was killed.

After such attacks, the Taliban, attempting to stir up anti-American sentiment in the region, routinely claims, falsely, that the victims are all innocent civilians. In several Pakistani cities, large protests have been held to decry the drone program. And, in the past year, perpetrators of terrorist bombings in Pakistan have begun presenting their acts as "revenge for the drone attacks." In recent weeks, a rash of bloody assaults on Pakistani government strongholds has raised the spectre that formerly unaligned militant groups have joined together against the Zardari Administration.

David Kilcullen, a counter-insurgency warfare expert who has advised General David Petraeus in Iraq, has said that the propaganda costs of drone attacks have been disastrously high. Militants have used the drone strikes to denounce the Zardari government -- a shaky and unpopular regime -- as little more than an American puppet. A study that Kilcullen co-wrote for the Center for New American Security, a think tank, argues, "Every one of these dead non-combatants represents an alienated family, a new revenge feud, and more recruits for a militant movement that has grown exponentially even as drone strikes have increased." His co-writer, Andrew Exum, a former Army Ranger who has advised General Stanley McChrystal in Afghanistan, told me, "Neither Kilcullen nor I is a fundamentalist -- we're not saying drones are not part of the strategy. But we are saying that right now they are part of the problem. If we use tactics that are killing people's brothers and sons, not to mention their sisters and wives, we can work at cross-purposes with insuring that the tribal population doesn't side with the militants. Using the Predator is a tactic, not a strategy."

Exum says that he's worried by the remote-control nature of Predator warfare. "As a military person, I put myself in the shoes of someone in FATA" -- Pakistan's Federally Administered Tribal Areas -- "and there's something about pilotless drones that doesn't strike me as an honorable way of warfare," he said. "As a classics major, I have a classical sense of what it means to be a warrior." An Iraq combat veteran who helped design much of the military's doctrine for using unarmed drones also has qualms. He said, "There's something important about putting your own sons and daughters at risk when you choose to wage war as a nation. We risk losing that flesh-and-blood investment if we go too far down this road."

Bruce Riedel, who has been deeply involved in these debates during the past few years, sees the choices facing Obama as exceedingly hard. "Is the drone program helping or hurting?" he asked. "It's a tough question. These are not cost-free operations." He likened the drone attacks to "going after a beehive, one bee at a time." The problem is that, inevitably, "the hive will always produce more bees." But, he said, "the only pressure currently being put on Pakistan and Afghanistan is the drones." He added, "It's really all we've got to disrupt Al Qaeda. The reason the Administration continues to use it is obvious: it doesn't really have anything else.".

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