Spoiler warning: Spoilers for the full film; discussion of sexual violence and suicide.
Augustus Landor murdered the cadets, while Lea and Artemus Marquis removed the hearts. The Pale Blue Eye has two overlapping crimes, which is why exposing the occult ritual does not identify the person who caused the deaths.
Why did Landor kill them?
His daughter Mattie died by suicide after being raped by cadets from West Point. The killings are his revenge. His account of her absence conceals the loss motivating the investigation he has accepted.
The ritual gives him an unexpected opportunity: another party interferes with the bodies, creating evidence that appears to point away from a bereaved father and toward a different kind of killer.
This makes his investigative skill part of the deception. He is capable of following clues while also understanding how their arrangement can shelter him.
Why does the heart-removal explanation fall short?
Lea hopes occult practices will cure her illness, with Artemus assisting her. Their actions explain the mutilations but not the original murders.
Poe’s final deduction depends on refusing to treat those answers as interchangeable. Solving what happened to a corpse is not necessarily the same as identifying who killed the person.
The distinction also changes Poe’s relationship with Landor. The investigator who gave him companionship has used that companionship inside a case built around his own guilt.
Does Landor die at the cliff?
The film leaves him at the place associated with Mattie’s death without showing him jump. Director Scott Cooper interprets the moment as movement toward accepting the loss and continuing to live.
That creator’s reading is useful context, but it should remain separate from the observable endpoint. The film does not supply a later life that proves what Landor does after leaving the frame.
The final disclosure solves the murders without restoring an innocent mentor for Poe. Landor’s grief is real, and the killings are still his choices. Holding both facts together explains why the ending is more painful than simply unmasking an occult murderer.
Sources: official ending breakdown.