The Pale Blue Eye

In October 1830, alcoholic retired detective Augustus Landor is asked by the military to investigate the hanging of Cadet Leroy Fry at the United States Military Academy. Landor is a widower whose daughter Mattie ran off two years before.
After Fry was hanged, his heart had been removed from his body. Examining the corpse, Landor finds a small fragment of a note in Fry's hand. Dr. Daniel Marquis, the examining physician, suggest that he did not hang himself but was murdered. Landor secretly enlists the help of Edgar Allan Poe, another cadet at the academy. Poe and Landor deduce that the note was summoning Fry to a secret meeting. After a cow and a sheep are found butchered with their hearts removed, it is suspected that the murder could be linked to black magic rituals.
Another cadet, Ballinger, is found hanged with his heart and genitals removed. A third cadet, Stoddard, disappears; Landor tells the authorities that he presumes Stoddard had reason to believe he was next in line to be killed. Landor and Poe suspect the family of Dr. Daniel Marquis, who performed the autopsy on Fry. Particular suspicion is on his son Artemus and his daughter Lea, who suffers from random seizures. Landor confronts Dr. Marquis, who admits that he resorted to black magic to cure Lea of her seizures.
Poe is drugged and finds Artemus and Lea about to cut out his heart in accordance with the ritual. Landor rescues Poe, but the building catches fire and Lea and Artemus die. Thinking that the case is solved, the military thanks Landor for his service. However, Poe confronts Landor with his realization that the handwriting on the note fragment in Fry's hand matches that of Landor. It becomes apparent that Landor was the killer of the cadets.
Two years earlier, Landor's daughter Mattie was raped by Fry, Ballinger, and Stoddard after attending her first ball. Traumatized, she killed herself by jumping off a cliff. Landor pretended that she ran away. Distraught, he set out to avenge his daughter. He left the note for Fry, luring him to a lonely spot before getting the other two's names out of him and hanging him. A patrol happened to walk by so he was forced to leave the body there. Lea and Artemus stole Fry's heart for their ritual. After killing Ballinger, Landor mutilated his corpse to make it appear that the cadet had been murdered by the same "madman" who desecrated Fry's body, whilst he hopes that - though he has been unable to kill Stoddard - the rape will remain on his conscience for the rest of his life.
Poe tells Landor he has two notes with handwriting samples that link Landor directly to the murders, but burns them instead. Landor later stands at the cliff where his daughter leapt to her death. He lets her hair ribbon float away in the wind, saying "Rest, my love".