Fethullah Gulen is the leader of the FETO network and a permanent resident of the United States.
His organisation has been designated as a terror group by Turkey.
Turkey has requested his immediate extradition.
According to the Turkish government, Fethullah Gulen and his network orchestrated the failed coup of July 15, 2016, which killed 249 people and injured 2,000 others.
Ankara also accuses FETO of being behind a long-running campaign to overthrow the state through the infiltration of Turkish institutions, particularly the military, police, and judiciary.
The 76-year-old has been living in self-exile for almost 20 years and from his hideout, and Ankara says he directs hundreds of thousands of his followers around the world.
TRT World's Ediz Tiyansan has the story.