Here a crazy therory from me. The virus didn´t really "kill" the people. Their Consiouness still remained in their corpses. They were actually "living deads". The Plutonian was the only one who could understand this, because he still could hear them. He decided, that it was impossible for them to live under normal humans any longer and brought them to his fortress. And there they lived with him. After some time they accepted their fate and in the end they became some sort of family for him. Till something happend and they died again. And this drove him over the edge.