Under custody for his alleged links to the July 15 foiled coup, Mümin Köroğlu, a former physics lecturer at Ankara Police College, was reportedly forced to make the much-politicized Rabaa sign, with his mouth taped by police officers.

First used by Muslim Brotherhood supporters to protest the military coup in Egypt in 2013, the four-finger hand gesture –dubbed Rabaa sign– have often been used by President Recep Tayyip Erdoğan during election rallies in Turkey. The sign has recently become a symbol of Erdoğan supporters.

According to WhatsApp messages obtained by Twitter account @Turkeyiniskence, Köroğlu had his mouth taped by police officers and was photographed making a Rabaa sign.

The lecturer’s son Muaz Köroğlu, also a former police officer, was killed during a traffic accident in Turkey’s eastern province of Şanlıurfa.

Turkey survived a bloody coup attempt on July 15 and state institutions has been undergoing an unabated purge as part of investigations into the attempt since then.

40,029 people from all walks of life have been detained with 20,355 of them arrested since the coup attempt. Some of the arrestees often appeared to have been tortured under custody.