I clearly understood that the choice of the Lubyanka station was to send a message to the FSB, but it is interesting to note that 1) the bombers could have selected a different station to claim more victims, and 2) the Park Kultury attack may have been aimed at FSB officers traveling to work on the red line. Now they will probably go back to using chauffeured BMWs.
From Russia Profile:
But terrorists could have targeted larger transport hubs. The reason they chose to bomb Lubyanka was “symbolic,” said Sergei Markedonov, an independent political analyst and Caucasus expert, because the FSB’s headquarters are based at Lubyanka. Meanwhile, the bomb at Park Kultury, four stops south of Lubyanka, was detonated on the Sokolnicheskaya line used by the FSB to get to work. “The timing as well – it’s the normal time for servicemen to be going to work,” said Andrei Soldatov, an independent security analyst. The Park Kultury bomb may also have been originally intended for the Oktyabrskaya metro station, one stop away, where the Interior Ministry headquarters are located.