Turkish police detained 20 people on 4 October in an operation centred on Konya and covering eight provinces, directed at what the authorities describe as the “military covert structure” of the Gülen movement. Five were remanded in custody and 15 released under judicial control.

The operation was carried out by the Counter-Terrorism Branch of the Provincial Police Directorate after what the pro-government daily Sabah describes as technical and physical surveillance.

Sabah gives the basis for the detentions in a single sentence. The 20 were, it reports, “found to have been called consecutively by members of the organisation and to be affiliated with FETÖ” — FETÖ being the designation Turkish authorities apply to the Gülen movement. Türkiye classes the movement as a terrorist organisation; other governments and international bodies do not.

No further evidence has been made public. Neither source names the eight provinces, identifies the prosecutor’s office, or states the occupation or former rank of anyone detained. No charges have been announced and nobody has been convicted.

What is described, therefore, is a set of incoming telephone calls, said to have been placed to the suspects by other people, in a pattern. Three quarters of those detained on that basis were released within a day.

The method has a history. “Consecutive calling” (ardışık arama) refers to the practice of inferring membership from patterns in call records, typically calls received from public telephones, on the theory that an organiser rang contacts in sequence. The person called is not alleged to have made the call, nor to have said anything in particular on it. In thousands of prosecutions since 2016 the pattern itself has been offered as proof of membership of an armed organisation.

The Grand Chamber of the European Court of Human Rights has already held that this approach to a different category of evidence breaches the Convention.