Final answer:
The author includes information about Dr. Roylett's violent past in India to create suspense and establish a motive for the crimes committed in the story.
Step-by-step explanation:
The author includes information about Dr. Roylett's violent past in India in order to create suspense and establish a motive for the crimes committed in the story. By revealing that Dr. Roylett was deeply involved in illegal activities in India, the author suggests that he may also be responsible for the violence in the present. This information adds to the mystery and keeps the readers engaged throughout the story.