Peter Bergen and David Sterman wrote for CNN about the likely perpetrators of the recent bombing in St. Petersburg's metro.
According to Russia authorities, Monday's suicide bombing on the St. Petersburg metro was carried out by Akbarjon Djalilov, 22, from Kyrgyzstan, a Central Asian republic of the former Soviet Union.
The fact that a second bomb was found at another St Petersburg metro station indicates that Djalilov was likely not acting alone and was part of larger conspiracy.
There are two groups that have both the capability and the intent to carry out large-scale terrorist attacks in Russian cities. First, there are Chechen separatists who have mounted a wide range of terrorist attacks in Russia. The Russians have been waging wars with these separatists since the 19th century, but for obvious reasons Chechen separatist terrorism tends to be carried out by Chechens.
The other, more likely perpetrator, ISIS has plotted to target St. Petersburg in the recent past.