<sod >Two people were believed to be behind the deadly attack in the subway in St. Petersburg, Russia, planting a total of two bombs, one of which exploded, state media reported Monday as police and anti-terror investigators raced to find the killers.< eod>< sod > One person was believed to be behind the deadly attack in the subway in St. Petersburg, Russia, planting two bombs, one of which exploded, state media reported Monday.< eod>