Making Sense of the Attack in St. Petersburg

Russia is no stranger to terrorist attacks. But for the past four years, the country (beyond its restive North Caucasus region) has been free of the kinds of large assaults that have periodically rocked Europe and the United States. Then on Monday, an explosion ripped through a subway train in St. Petersburg, killing 11 people and injuring nearly 50 more. (A second device was reportedly found and dismantled at a nearby metro station.) Russia's Investigative Committee quickly declared the incident a terrorist attack, and media outlets across the country have proposed different theories to explain who staged the attack and why. Though some scenarios are more plausible than others, each comes with its own set of consequences for the Kremlin and the country....