However, here's a brief note on the attacks, specifically in answer to a question about how the Russian investigators will be able to identify the attackers:
No, unless there is some surprisingly good CCTV video footage available, it is unlikely that a recognition could be made from that alone. Instead, one can almost always find the heads of the bombers intact after the detonation of an explosive vest.
In a televised meeting with President Dmitry Medvedev, Federal Security Service head Alexander Bortnikov said body fragments of the two bombers pointed to a Caucasus connection. The bombers have not been identified and Bortnikov did not elaborate.That and some basic legwork on who was seen with who by surviving witnesses (and the CCTV) will likely leave a trail back to an identification... and maybe finger the accomplices.
Good hunting, ФСБ.