An Ankara court remanded 39 former police officers in custody early Saturday morning as part of a probe into the Fetullah Terrorist Organization (FETO).
According to Ankara's Chief Public Prosecutor's Office, 51 former police officers were brought to court to provide testimony.
The suspects were allegedly using the ByLock mobile phone messaging app which FETO members used to communicate with each other during last July's defeated coup.
The app is believed to have been cracked by Turkish security agencies, allowing them to identify tens of thousands of FETO supporters.
The 12 remaning suspects were released under judicial control.
Ankara accuses FETO and its U.S.-based leader Fetullah Gulen of having orchestrated the defeated coup of July 15, 2016, which left 250 people martyred and nearly 2,200 injured.
