MOSCOW — Vladimir Putin vowed Tuesday to "drag out of the sewer" the masterminds of the twin suicide bombing of the Moscow subway system that killed 39 people and left scores wounded. The powerful prime minister spoke as Russia mourned the dead from Monday's attacks; teary passengers lit candles and left carnations at both of the central stations that were hit. The blasts shocked a country that had grown accustomed to such violence being confined to a restive southern corner – and marked the return of terrorism to the everyday lives of Muscovites after a six-year break. As senior politicians call for the return of the death penalty, the attacks have raised fears that civil liberties may again be sacrificed under the pretext of fighting terrorism – a charge Putin faced during his eight-year presidency. "I understand what authorities will do.