The payments, uncovered by researchers after the raid in which he was killed, were made to members of Hurras al Din, an unofficial affiliate of Al Qaeda and an enemy of the Islamic State.

While the rival group kept his secret, Mr. al-Baghdadi was ultimately betrayed by a close confidant, two American officials said, leading to his death in an American Special Forces raid last weekend.

Other new details: During the raid, American forces recovered a number of laptops, cellphones and thumb drives from the compound, whose data could provide another window into the organization.

And according to the Pentagon, six other people were killed in the compound, aside from Mr. al-Baghdadi and the two children he took with him when he detonated a suicide vest.

The informant: The identity of the individual, recruited by the intelligence arm of the Kurdish-led militia allied with the United States in the fight against the Islamic State, has not been revealed because of safety concerns. But one person with knowledge of the events described the informant as someone who is “a very, very close, trusted confidant of Baghdadi’s.”