Syrian Democratic Forces (SDF) leader Mazloum Abdi has said that his forces began gathering intelligence on Baghdadi's whereabouts five months ago, according to The Washington Post.
In mid-2019, Reuters reports, Iraqi, US, and Turkish intelligence officials were able to nail down Idlib as the location of Baghdadi's hideout after capturing five senior ISIS leaders who told them locations where they were meeting Baghdadi.
Informants within Syria then found Ethawi at a market in Idlib and followed him to the house where Baghdadi was staying.
"We passed the details to the CIA and they used a satellite and drones to watch the location for the past five months," an Iraqi security official said.
Intelligence from former al-Qaeda affiliate Hayat Tahrir al-Sham (HTS), which controls the area surrounding Idlib, may have aided in Baghdadi's capture, too, Reuters reports.
A jihadi commander in Idlib said HTS had captured Abu Suleiman al-Khalidi, a close aide to Baghdadi. HTS is believed to work with Turkish forces in northwest Syria; information from Khalidi may have been passed on to other intelligence agencies.
Around the same time, The Washington Post reports, a disaffected ISIS member began to leak information to the SDF; as the US became more confident in the informant's credibility and put his intelligence together with additional information they had uncovered, the plot to capture or kill Baghdadi came together.