On Sunday, an unmanned CIA aircraft hovering far above the vast Yemeni desert fired a missile that incinerated a car carrying six men accused of plotting to kill Americans.
The attack on Qaed Sinan Harithi, reputed to be the leader of al-Qaida in Yemen, and the five men riding with him was partly retaliation. Harithi is believed by U.S. intelligence to have organized the bombing of the USS Cole in the port of Aden, which killed 17 U.S. sailors in October 2000.
But this attack was also partly prevention. It combined the Bush administration's new doctrine of pre-emption of terrorism with the stealth technology of a Predator drone, which can lurk unseen three miles in the air, transmitting live video or radar images thousands of miles to an operator, who can shoot the drone's Hellfire missiles by pushing a button.
For some, the attack raises difficult legal and policy questions about the war on terror.
"It's a highly lethal machine the CIA is using to carry out assassinations," says Loch K. Johnson, a University of Georgia political scientist who has advised Congress on intelligence reform.
"If you're going to accuse someone of being a terrorist, should you present some evidence? Should you arrest them and give them a trial? Is America going to send drones into any country we choose to kill people we think are terrorists?"
At the least, Johnson says, there should be congressional oversight and public discussion of policies on such attacks.
"I think these questions merit much closer attention than they've received," Johnson says.
In contrast, Larry Taulbee, a political scientist at Emory University, says the attack - in which the Yemeni government apparently cooperated - was justified and might well prove effective in deterring terror.
"There's a self-defense case to be made here," he says. "Clearly it's going to make the leadership of al-Qaida a lot more cautious. ... If you can make the leaders and organizers fearful, it's going to make their terrorist operations a lot more difficult."
Still, Taulbee says, the effect of such attacks in disrupting or deterring al-Qaida might be offset by opposite effects - provoking retaliatory attacks on U.S. targets or recruiting new, young militants into al-Qaida.
The complex implications of such surprise attacks were illustrated by the news yesterday that one of the six men killed was an American. He was identified by an unidentified "security source" speaking to the Associated Press as Ahmed Hijazi, also known as Jalal, but no details on his background or U.S. citizenship could be learned.
Asked about the report yesterday, a U.S. official would say only: "All of those in that car were either al-Qaida members or supporters."
The use of targeted killings as a tool of foreign policy is not new in American history. The CIA plotted in the 1950s and 1960s to kill several foreign leaders, including Cuban leader Fidel Castro. There is evidence that President Dwight D. Eisenhower approved a CIA plan to kill Patrice Lumumba, the first prime minister of the Republic of the Congo, and the CIA station chief received poison to use for the job. Lumumba was killed by rivals in 1961 before the plan could be carried out.
As a result of the controversy over such plots, President Gerald Ford banned assassination in 1976, reasoning in part that the open nature of American society would make U.S. officials particularly vulnerable if assassination became a widespread practice.
But subsequent presidents have found ways to skirt the ban. President Ronald Reagan, explaining the bombing of Libyan leader Muammar el Kadafi's compound in 1986, said the goal was not to kill him, but added: "I don't think any of us would have shed any tears if that happened." Similarly, the first President Bush approved attacks on Saddam Hussein's Baghdad palace during the Persian Gulf war.
The ban has not been considered to apply to terrorists. After the bombings of two U.S. embassies in East Africa in 1998, President Clinton responded with cruise missile attacks on a supposed chemical weapons plant in Sudan and a terrorist training camp in Afghanistan where Osama bin Laden was believed to be at a meeting.
No evidence of chemical weapons was found at the plant, and bin Laden had left the meeting before the missiles hit. Some experts on al-Qaida believe the failed attempt to kill bin Laden greatly elevated his status in the Muslim world.
Such long-term strategic considerations, as well as short-term benefits, must be considered in judging attacks like the one in Yemen, says Kenneth Roth, executive director of Human Rights Watch. Tactics in the war on terrorism already are depriving the United States of the moral authority it once had in criticizing other nations for human rights abuses, he says.
Roth, a former federal prosecutor, says the U.S. government has a duty to use law enforcement against terrorists when it is possible - though he acknowledges it might not have been feasible to arrest the Yemeni men and bring them to trial.
"It's very important that the United States articulate not only the rationale for what it did in Yemen but the limits to such actions," Roth says. "Could the U.S. have summarily shot [al-Qaida ally] Jose Padilla as he stepped off the plane at O'Hare? To give an absurd example, could the CIA have used a Predator to take out the al-Qaida cell in Hamburg, Germany? If the U.S. declares it has the right to kill anyone it designates an enemy combatant, it would open a huge and dangerous hole in human rights protections."
The technology of killing has advanced enormously since the poisons and exploding cigars of the 1960s. But it remains imperfect, as the accidental killing of civilians during the war in Afghanistan showed.
In one instance in February, an Afghan peasant was targeted by a CIA Predator because his tall stature made the drone operator think he might be the 6-foot-5 bin Laden. But local villagers interviewed by reporters after the tall man and two companions were killed by a Hellfire missile said they were peasants scavenging for scrap metal.
Similar mistakes have been made on occasion by Israel, which has carried out numerous targeted assassinations of suspected terrorists in recent years - despite U.S. protests.
This week U.S. officials said the criticism of Israel is consistent with the attack in Yemen, because the Palestinians have representatives willing to negotiate while al-Qaida does not.
Mark Regev, a spokesman for the Israeli embassy, says his country approves of the U.S. attack in Yemen and sees no important difference from Israel's targeted killings:
"I would argue that al-Qaida, Hezbollah and Hamas are different manifestations of the same phenomenon - extreme, totalitarian Islamic terrorism. There's no such thing as good terrorism and bad terrorism."