Sororicide

Sororicide (from Latin "soror" "sister" + "-cide", from "caedere" "to cut, to kill") is the act of killing one's own sister.

There are a number of examples of sororicide and fratricide (the killing of one's brother) in adolescents, even pre-adolescents, where sibling rivalry and resulting physical aggression can get out of hand and lead to the death of one of them, particularly if a firearm is available or if one is significantly older than the other and misjudges his/her own strength.

Compare with child murder (the killing of an unrelated child), infanticide (killing of an infant under the age of one year), filicide (the killing of a child by his or her parent), and patricide and matricide (the killing of a father or mother respectively by his or her child).

Known or suspected sororicides

* Berenice IV of Egypt is believed to have poisoned her sister Cleopatra VI Tryphaena in 57 BC. She was later beheaded on the orders of her father, Ptolemy XII.
* Cleopatra of Egypt requested the execution of her sister, Arsinoe IV, which was carried out under the orders of her lover Mark Antony in 41 BC.
* Roman Emperor Caligula, according to historian Suetonius, killed his sister Drusilla after learning that she was pregnant with his child in 38 AD. Most historians now believe that she probably died of fever.
* Roman Emperor Commodus ordered his older sister Lucilla to be put to death in 182 AD, after she was implicated in plots with members of the Senate to overthrow him.
* Dipendra of Nepal (1971-2001) massacred much of his family at a royal dinner on June 1, 2001, including his father, mother, brother, and sister Princess Shruti.
* Ronald DeFeo, Jr. shot his two sisters, Allison and Dawn, in 1974. Their murders became the inspiration for the Amityville Horror books and films.
* Canadian serial killers Karla Homolka and Paul Bernardo raped, then accidentally murdered Karla's sister Tammy (1990).
* Yuki Muto murdered his sister Azumi Muto on December 30, 2006 in Japan.

ororicides in fiction

* In William Shakespeare's "King Lear", Goneril poisons her sister Regan in their struggle for power.
* In the " Halloween" film series, serial killer Michael Myers relentlessly pursues and slays both his older sister, Judith, and his younger sister, Laurie.
* In the "God of War" (video game) series, Kratos accidentally murders Athena, where he learns she's Kratos's half-sister because it was revealed that Zeus is his birth father.
* In the 1962 movie "What Ever Happened to Baby Jane?" (as well as the 1991 TV movie "What Ever Happened to Baby Jane?"), sisters Blanche and Jane mistreat and attempt to kill each other out of jealousy and hatred.
* According to Roman mythology, one of the Horatii killed his sister after she mourned an enemy he had slain, who had happened to be her fiancé.
* In the anime "Blood+", Chiropterans have a biological hive system. Two twin Queens are always born from cocoons in one of the preceding Queen's womb. When the blood of one Queen mixes with her sister's, it violently crystallizes. In "Blood+", Saya kills her twin sister Diva in a 123 year-old war between them.
* In "", the village forces twin sisters to partake in a ritual in which one sister strangles the other. In the canonical 'bad ending', Mio Amakura does indeed strangle her twin sister Mayu to death. (The other documented instance of sororicide is when Azami Kiryu kills her sister Akane.)
*In Child Ballad #10, "The Twa Sisters", or "The Dreadful Wind and Rain" the older sister murders the younger sister over the love of a man, and the younger sister's bones are found by a wandering musician who makes an instrument (either a harp or a fiddle, depending on the version) out of them and strings it with her hair. The instrument then tells the story of how she died, usually resulting in a gruesome death for the older sister.
*In "", Dahlia Hawthorne kills her step-sister Valerie Hawthorne in the fourth case of the game when Valerie threatened to expose the truth behind a fake kidnapping that Dahlia and her boyfriend plotted five years ago in order to steal a rare diamond.
*In one of the endings of the video game, Trapt (video game), Allura kills her half-sister, Rachel, for the final sacrifice to revive Malphas. Also, Finnegan kills his older sister Ada in an act of betrayal after being corrupted by the desire to obtain Allura's power for himself.
*In the anime Death Note, Light Yagami considers killing his sister, Sayu when she ends up being captured by Mello (Death Note) and his gang in an attempt to retrieve the titular Death Note, but Light doesn't kill her simply because he could not blame her death on Kira.
*In the anime Code Geass, Lelouch Lamperouge kills his half-sister Euphemia li Britannia in order to stop a massacre that he accidentally ordered her to start. Also, Schineizel guns down his sister Cornelia after revealing his plans to rule the world as a god.
*In the horror film Catacombs (film), a deranged Victoria kills her sister Carolyn in a rage after being yelled at over the accidental murder of Jean-Michael.