"This terrorist attack was committed by one of the radical Islamist terrorist communities. It was especially difficult to identify them due to the fact that the mastermind, organizers and performers of the terrorist attack were not even familiar with each other and kept in touch with the help of modern means of communication," Petrenko said.
A thorough analysis of the so-called electronic traces of such communication method that allowed to identify all the members of the criminal group in the shortest time possible, she noted.
As many as 11 people were identified as the attack's participants, all of them are being held in custody, Petrenko added.
An explosion hit a train between the Sennaya Ploshchad and Tekhnologichesky Institut-2 stations in the St. Petersburg subway on April 3 last year, killing 16 people, including the perpetrator identified as Akbarzhon Jalilov, and leaving about 50 people wounded. Another explosion, at the Ploshchad Vosstaniya station, was prevented due to the timely detection of an improvised explosive device.