Shortly before the United States and Israel were poised to launch an attack on Iran, the C.I.A. zeroed in on the location of perhaps the most important target: Ayatollah Ali Khamenei, the country’s supreme leader.

The C.I.A. had been tracking Ayatollah Khamenei for months, gaining more confidence about his locations and his patterns, according to people familiar with the operation. Then the agency learned that a meeting of top Iranian officials would take place on Saturday morning at a leadership compound in the heart of Tehran. Most critically, the C.I.A. learned that the supreme leader would be at the site.

The United States and Israel decided to adjust the timing of their attack, in part to take advantage of the new intelligence, according to officials with knowledge of the decisions.

The information provided a window of opportunity for the two countries to achieve a critical and early victory: the elimination of top Iranian officials and the killing of Ayatollah Khamenei.

The remarkably swift removal of Iran’s supreme leader reflected the close coordination and intelligence sharing between the United States and Israel in the run-up to the attack, and the deep intelligence the countries had developed on Iranian leadership, especially in the wake of last year’s 12-day war. The operation also showed the failure of Iran’s leaders to take adequate precautions to avoid exposing themselves at a time where both Israel and the U.S. sent clear signals that they were preparing for war.

The C.I.A. passed its intelligence, which offered “high fidelity” on Ayatollah Khamenei’s position, to Israel, according to people briefed on the intelligence.