It seems the man who cured the globe cannot stop his own extinction
Rotti had received (in the beginning of the movie) a clipboard from his doctors saying that he was dying, and he can't do anything about it, even though he's the owner of Geneco.
He (Rotti) is talking to Marni (her spirit), explaining why he had to kill her and why he had poisoned her. She knew too much when she and Nathan got together and had a baby.