Turkish security forces on Sunday arrested a foreigner in Istanbul believed to be ISIS’s military leader and have ties to dead ISIS leader Abu Bakr al-Baghdadi.

The Afghan national, who goes by the nickname “Asim,” has been dubbed the right-hand man of al Baghdadi. Turkish security authorities arrested him in the Atasehir district on the city’s Asian side. He had been traveling on a fake passport, according to a statement released by the police.

Asim had disappeared months after the terrorist group was overrun in Syria and Iraq in December 2017. Before that he had helped hide al-Baghdadi, Turkish intelligence and security officials told the news media.

Al-Baghdadi was killed when he detonated a suicide vest during a raid by U.S. Special Operations troops in 2019 on his sanctuary in Syria’s Idlib province.