fratricide -
The intentional or unintentional killing of a comrade in arms.
Wikipedia
Fratricide is the act of a person killing his or her brother. According to the Bible and the Qur'an, fratricide was the first type of murder committed in human history. Related concepts are sororicide (the killing of one's sister), child murder (the killing of an unrelated child), infanticide (the killing of a child under the age of one year), filicide (the killing of one's child), patricide (the killing of one's father), matricide (the killing of one's mother), mariticide (the killing of one's husband) and uxoricide (the killing of one's wife). See also siblicide.