Terrorists used Threema app?

Terrorists at the Holey Artisan Bakery used a secured messaging app, Threema, to send messages and upload pictures of their victims after they had been shot and hacked with machetes, reports Times of India.
However, the daily did not mention any source.

A secure messaging system, Threema deletes messages from servers, leaving little trace and preserving anonymity.

This has made it difficult for Bangladesh authorities to get forensic clues about that night. Bangladesh authorities are unearthing more links between the attackers and terror group, Jamaat-ul-Mujahideen Bangladesh (JMB), the report added.

Benazir Ahmed, director general of Rapid Action Battalion (RAB) told Times of India, "Investigations are on... from the primary information available we can say these people have links with JMB."