According to Russia's Investigative Committee, at least 4 kilograms (8.8 pounds) of TNT was used in the latest attack, causing the complete destruction of the bus and shattering the windows of a few nearby buildings. The bomber was reportedly Pavel Pechenkin, a former paramedic who joined the Dagestani militant movement in 2012. The explosive device reportedly contained the same kind of metal fragments as the explosive device in the Dec. 29 bombing, and both blasts targeted public transportation infrastructure in a city that is a large transportation hub. The timing and similarities in materials and targets suggest that the bombings were linked and coordinated.
There are several possible reasons for the attacks in Russia's southern city. First, Volgograd (formerly Stalingrad) is a common target for militants from Russia's Northern Caucasus because it is the largest ethnically Slavic city close to the Muslim Caucasus belt. It is also the largest Slavic city near Sochi, where the Olympics will be held. It is increasingly difficult for militants to strike large targets in faraway destinations such as Moscow, and the Muslim communities in the capital are increasingly under threat of ethnic purges and would prefer not to attract attention or be cast as militants.
This week is also the start of the Russian holiday season. New Year's is this week and the Russian Orthodox Christmas is next week. As a result, transit at bus and train terminals is particularly heavy.
The Caucasus Emirate militant group identified the Sochi Olympics as a major target, so it would seem that the group would save its larger assets and resources until the games are closer. In addition, Russia has shown in recent months that it is becoming more active in pre-empting terrorist operations — a common security tactic in the run-up to large world events in an effort to prevent disruptions. It is therefore possible that the militants' larger operations were already penetrated, leaving them with only the ability for smaller attacks against soft targets. The militants could also have been concerned that the Volgograd suicide cell was about to be penetrated, and thus they decided to utilize their assets now before they could be arrested.
Finally, the attacks in Volgograd could be intended to draw Russian security resources and attention away from larger targets such as Moscow or Sochi, potentially providing other militants the opportunity to attack and disrupt the Olympics.
The militants' short-term goal with these attacks is to show that Russia is not safe for its own people or travelers. However, the long-term goal of the Caucasus militants has been the same throughout history: to force the Russians to draw down their presence in the Muslim Caucasus. Throughout Russia's history, Muslim insurgents from the Russian Caucasus have tried to make Russian occupation of their lands so painful that it would not be worth the effort to hold the lands. But as Russia has shown for hundreds of years, it will not give up land that it sees as imperative to its foundation.