Episode 77 of "Cold Case"
s04e08 Fireflies

When a mailman is found dead in his home, several bags of undelivered mail are discovered, including a letter postmarked 31 years ago and is now a major piece of evidence in the 1975 case involving a missing girl. Lilly and the detectives learn that the missing girl, Melanie, was abducted from her bedroom window and her best friend's, Cherise, brother was the number one suspect. The case takes shape when postal workers from 1975 admit that they would not deliver mail to the Black families in the neighborhood and did not like the friendship between Melanie and Cherise. In 1975, racial discrimination made everyone a suspect and now Lilly and the team must find out what really happened to Melanie.