The European Court of Human Rights (ECHR) held Turkey responsible for unfair trial violations in a landmark judgment Tuesday concerning criminal convictions based on use of the encrypted messaging application ByLock .

ByLock came under scrutiny from Turkish authorities following the failed 2016 coup attempt. The government alleged the app was used exclusively by supporters of Fethullah Gülen, an Islamic cleric living in exile whom Turkey accuses of masterminding the coup. In 2017, Turkey’s constitutional court ruled that using ByLock could be considered evidence of membership in a terrorist organization. This established a legal framework where anyone found to have downloaded the app, regardless of message content, faced terrorism charges.

In the case of Yüksel Yalçinkaya v. Turkey, the Grand Chamber of the ECHR ruled that Turkey violated Yalçinkaya’s fair trial rights under Article 6 of the European Convention on Human Rights, as well as his rights against retroactive criminalization under Article 7. Yalçinkaya, a former teacher, had been convicted in Turkish courts of membership in an armed terrorist organization solely on the prosecutors’ assertion that he used the ByLock app.

However, the ECHR found flaws in how Turkish courts handled evidence related to ByLock usage. The ECHR held that Turkish courts equated mere use of the app with criminal intent without properly establishing the elements of the offense. The courts also denied Yalçinkaya access to key encrypted data that could have allowed him to challenge the evidence.

In the ECHR’s view, such an overly broad interpretation created an “almost automatic presumption of guilt” contrary to the object of Article 7, which protects against arbitrary prosecution. The judgment further stated Turkish courts failed to implement sufficient safeguards for Yalçinkaya to effectively question the evidence, violating his fair trial rights under Article 6.

Notably, the court held the problems identified were “systemic in nature,” given over 8,500 similar cases pending at the ECHR and 100,000 suspected ByLock users in Turkey. Under Article 46, the court ruled Turkey must adopt general measures to address the systemic issues surrounding its judiciary’s approach to ByLock evidence.

However, Turkish Justice Minister Yilmaz Tunc sharply criticized the ruling, claiming the ECHR exceeded its powers by directly evaluating evidence which national courts deemed sufficient. Tunc said prior ECHR case law reserves evidence admissibility questions strictly for domestic jurisdiction.

The landmark judgment increases scrutiny on Turkey’s mass trials of alleged Gülen supporters, but it remains to be seen if Ankara will implement reforms to its judiciary’s ByLock evidence practices or challenge the ECHR’s authority on this issue further.