Russia faces yet another investigation into an atrocity on its public transport system.
In 2010 the Moscow metro was attacked
Two female suicide bombers from the restive Dagestan region detonated devices on separate trains during morning rush hour at least 40 people died with 100 injured.
In January 2011 the international arrival hall of Moscow’s Domodedovo airport was targeted by a single, male suicide bomber allegedly from the North Caucasus.
The explosion killed 37 people and wounded 173 others.
Russian authorities concluded that the violence was aimed “first and foremost” at foreign nationals.
In 2013 the public transport system of Volgograd was the scene of carnage on two consecutive days.
On December 29 a suicide bombing took place at the Volgograd-1 station killing 18 and wounding at least 44.
Confusion over the perpetrator or perpetrators abounded.
One day later second suicide bomber blew up a trolley bus in the same city killing sixteen people and injuring 41.
Russian authorities claim the attack was carried out by the Kadarskaya group based in Dagestan.
Federal Security Forces killed four suspects in a raid.
Authorities remain vigilant in February last year police arrested seven individuals in Yekaterinburg in the Urals accused of plotting attacks and possession of explosives.