St Petersburg metro explosion WHO? and WHY?

TASKS KEYS At least 14 people were killed in a blast on the St. Petersburg metro on April, 3rd. Alongside the dead, 51 people were injured in that shattering terrorist attack. Who was behind? What aims did they pursue? По вопросам сотрудничества и частных занятий teachandlearn@ С уважением, Игорь Чичикин