7 kilograms of TNT caused Friday night's derailment of a Russian Nevsky express train (Невский Экспресс) on its way from Moscow to St Petersburg. That's acording to Russia's FSB. At least 26 people have been confirmed dead, while 18 people are still unaccounted for. More than a hundred have been injured. Investigators believe it was a terrorist attack, and if proven, it would be the deadliest in Russia, outside the Northern Caucasus, in recent years.