ISTANBUL (AP) — The chair of Fenerbahce, one of Turkey’s leading sports clubs, was called to give testimony Saturday as part of an ongoing drug investigation involving high-profile entertainment and media figures.

Sadettin Saran, who holds dual Turkish and U.S. citizenship, gave a statement in Istanbul after returning from abroad before being sent to a forensic medical facility to have hair and blood samples taken, the state-run Anadolu news agency reported.

More than a dozen people have been detained since the start of December as part of an investigation overseen by Istanbul Chief Prosecutor’s Office.

TV news anchors, journalists, singers, actors and social media influencers have been among those detained on charges including the manufacture and trafficking of drugs and facilitating prostitution. Many have undergone blood and hair tests for the presence of narcotics.

Denver-born Saran, who was voted Fenerbahce’s chair in September, was questioned on suspicion of providing and facilitating the use of narcotic substances, according to Anadolu.

He returned to Caglayan courthouse after giving medical samples and was later released under judicial condition.

Istanbul-based Fenerbahce is one of Turkey’s most popular and successful sports franchises. The club’s former president Aziz Yildirim spent more than a year in jail in 2012 on match-fixing charges, before being acquitted when a new trial found the earlier case had been influenced by corrupt judges, prosecutors and police officers.

The club has also found itself caught up in a separate investigation into match-fixing across Turkish soccer.