...When Barak reactivated targeted killings in 2000, he said, "the first were urgent, but after, I said, 'We need rules.' " An aide exhumed four typed pages in a dusty, plastic sleeve, Barak said. They were the rules of engagement for the avengers of the 1972 Munich massacre.

Barak also secretly asked Daniel Reisner, a legal adviser to Arab-Israeli peace talks, to determine whether targeted killings were legal. Reisner agonized for six weeks. "It was a feeling of -- what on Earth has happened?" Reisner recalled. "Instead of two states living amicably side by side, I have to write opinions on how and when we kill each other."

Reisner concluded it was legal, with six conditions: that arrest is impossible; that targets are combatants; that senior cabinet members approve each attack; that civilian casualties are minimized; that operations are limited to areas not under Israeli control; and that targets are identified as a future threat. Unlike prison sentences, targeted killing cannot be meted out as punishment for past behavior, Reisner said. In 2002, a military panel established that targeting cannot be for revenge, but only for deterrence. A panelist said it took six months and 20 meetings to reach that conclusion.

"It's not an eye for an eye," Dichter said. "It's having him for lunch before he has you for dinner."...