Final answer:
The narrator's sister is the one who informs about Luis Enrique's murder by conveying the news of his death from AIDS-related complications.
Step-by-step explanation:
The person who tells about the murder of Luis Enrique is the sister of the narrator. The narrator remembers a specific moment in October of 1985, when their sister called to convey the tragic news that Enrique, someone the narrator had previously dated in Wisconsin, had passed away due to complications related to AIDS.