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.

Following Arim’s arrest, Turkish national television NTV posted a photo on Twitter of Arim. In the photograph, he appears as a balding, bearded man in a white jacket. The photo contrasts sharply with an earlier photo of him showing a long-haired, heavily bearded man in military fatigues waving a curved sword.

NTV added that after the joint operation by the National Intelligence Organization (MIT) and the Istanbul police, Asim is being interrogated by intelligence officials.

According to reports from the state-run Anadolu and Demiroren news agencies, Asim was suspected of organizing training for Islamic State fighters while in Syria and Iraq and of serving on ISIS’s decision-making council.

The Islamic State has conducted several attacks across Turkey, including on a nightclub in Istanbul on January 1, 2017, where 39 people were killed, and a bombing in the city’s historic district that killed 12 people in 2016.