SAME MOTIVATOR

The Russian Foreign Ministry have hinted at who it believes is behind the recent terrorist attacks in Volgograd:

Russia's Foreign Ministry likened the Volgograd bombing to “terrorist attacks” in the US, Syria or elsewhere, organized by groups with the “same motivator”, and vowed not to retreat.

[source : Consecutive Volgograd suicide bombing kills at least 14 (PHOTOS, GRAPHIC VIDEO), Russia Today, http://rt.com/news/russia-volgograd-trolley-blast-957/, 30th December 2013]

The general suspect is al Qaeda.

But al Qaeda is controlled by:
1. MI6
2. CIA
3. KSA

And if you wanted a name then Prince Bandar bin Sultan would suffice. He threatened Putin with this and other events, which over a period of 5 months have occured.