THE HORRIFIC shooting last month in London of an innocent Brazilian man, Jean Charles de Menezes, gives a chilling edge to guidance issued only days earlier by the International Association of Chiefs of Police about confronting suicide bombers. The guidance adopts a looser attitude toward the use of deadly force: In suicide bombing cases, officers should use force not only when the threat of someone's death is imminent but when they have a "reasonable basis to believe that the suspect has the capability to detonate a bomb." And when they need to shoot, officers should aim "at the bomber's head." British police, who chased Mr. Menezes into a subway car, jumped on him and then shot him repeatedly in the head, behaved much as the guidance suggests, under a similar British order -- the result being the death of a bystander.

A London-like disaster here, much as Americans might hope otherwise, is no longer unthinkable. For possible suicide bombing cases, U.S. Capitol Police officers have been retrained to shoot at the head as well. The idea is that when bombers have explosives strapped to their chests, a disabling shot to the torso is not a viable option. It can detonate volatile explosives or it can leave the bomber alive and capable of detonating them himself. Tasers can also set off the bomb. So if lethal force is necessary to stop a suicide bomber, it has to be a killing shot away from the torso -- that is, a shot to the head.

But as the London tragedy shows, accurately identifying a suicide bomber with split-second timing is difficult. And shoot-to-kill mistakes are irreversible. The guidance from the police chiefs organization, citing a number of characteristics, profiles a likely suicide bomber as someone wearing "heavy clothing no matter what the season," walking robotically with the appearance of drug use, carrying a backpack and making evasive movements, or "keeping a hand in the pocket." Washingtonians frequently see homeless or mentally ill people who meet this description. And like Mr. Menezes, such people might run from police rather than stop.

The head-shot order has its origins in Israeli practice. But the lessons of the Israeli experience with suicide bombings are not exclusively about the best way to kill would-be bombers. Israeli police are reported to have behaved with great restraint when confronted by explosives-laden Palestinians. In numerous instances, they have isolated potential bombers and disarmed them, sometimes at great peril to officers. And officials say they have shot a potential bomber dead only when an officer was unable, in a physical struggle, to disable him -- and in no circumstance in which the supposed bomber turned out to be a bystander. The key lesson here is that with rigorous training, authorities can learn to identify suicide bombers with greater accuracy, and to disarm them in most instances without killing. Shooting to the head may be a necessary last resort, but if through rash actions and poor judgment innocent people end up as the victims, the main battle has already been lost.