Baghdad, Iraq (CNN) Iraq intelligence agents tracked ISIS leader Abu Bakr al-Baghdadi for years before getting the break they say was critical to cornering him.

That break was the arrest in May of one of al-Baghdadi's brothers-in-law, Mohammed Ali Sajet al-Zubaaei, who joined ISIS in 2015 and had become one of the leader's trusted guides.

It was a culmination of Iraq's tactic of following al-Baghdadi by looking for those closest to him, said Lt. Gen. Saad al Allaq, the head of Iraq's military intelligence directorate.

"We were observing the movements of al-Baghdadi in indirect ways through his family," al Allaq said in a rare interview. "By doing that, it gives us some sort of secrecy and we gave al-Baghdadi an impression that we were not monitoring his movements."

Iraqi military intelligence launched its Operation Falcon Eye against al-Baghdadi after he declared the ISIS caliphate from Mosul.

Al-Zubaaei had helped al-Baghdadi avoid the authorities when he traveled. After he himself was captured by the Iraqis on the outskirts of Baghdad in May 2019, he provided crucial information, Iraqi intelligence officers told CNN.

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