The "interesting story" you're referring to is likely the episode " Cradle to Grave " (Season 5, Episode 5), which is widely considered one of the series' most disturbing and memorable "unsub" (unknown subject) cases.
You can watch the full episode on platforms like Apple TV or Philo . [S5E5] Cradle to Grave
Subplot-wise, this episode features Chief Hotchner being unusually hard on Derek Morgan, a move later revealed to be a test to see if Morgan is ready to lead the team. The "interesting story" you're referring to is likely
S5E5 - “Cradle to Grave” - Unsubs: A Criminal Minds Podcast S5E5 - “Cradle to Grave” - Unsubs: A
The BAU (Behavioral Analysis Unit) travels to Albuquerque, New Mexico, to investigate a series of young women who have been found dead shortly after giving birth. The victims are consistently troubled, blonde teenagers who have been missing for years. The investigation reveals a chilling pattern:
The victims are kept in a basement, well-fed and cared for only until they give birth. Immediately after delivery, the mother is murdered.
The couple is trying to "replace" their lost son. They keep the male babies that meet their specific criteria and discard the mothers and "imperfect" infants. Why It’s Notable