Og gosh, it is easy! You have to buy lots of arrows and crossbow in Vienna just before You go back to Prague and give it Wilhelm or Serena. Before You enter the room with Vozhd, You take the arrows and change the sword for the crossbow. Next, stand in front of the door where Vozhd lives and kill him with arrows all the time, so You even don't have to use blood etc. Arrows are expensive when You must buy lots of them, but You shouldn't care about it, because in London, You lose earned money.
I apologise for the bad English
