While it's not clear who carried out the deadly attack on the St. Petersburg metro, there are two groups that have both the capability and the intent to carry out large-scale terrorist attacks in Russian cities.
원문출처 : http://www.cnn.com/2017/04/03/opinions/russia-terror-attack-opinion-bergen-sterman/index.html
원문출처 : http://www.cnn.com/2017/04/03/opinions/russia-terror-attack-opinion-bergen-sterman/index.html