Overall, this seems like another predictable whodunnit … but that’s far from the truth.
As it turns out, Landor is the killer in The Pale Blue Eye. He spends much of the film mourning, claiming his daughter Mattie ran away with a man. However, Poe eventually figures out the truth, and Landor confesses: Mattie was raped by three cadets at the Academy Ball, which drove her to take her own life.
Source: https://www.distractify.com/p/who-is-the-killer-in-the-pale-blue-eye