Turkish President Recep Tayyip Erdogan once had a staunch ally in Muslim cleric Fethullah Gulen. But the relationship between the two men soured to the extent that the Pennsylvania-based preacher is now on Turkey's most-wanted list, accused of terrorism. Gulen has been in self-imposed exile in the United States since 1999. Our US correspondents went looking for him and his supporters in Pennsylvania.
A programme prepared by Patrick Lovett, Laura Burloux and Claire Pryde.