Kofer as atonement: Makkot 2b
The idea of Kofer is that the Damager removed from the Victim the opportunity to do Mitzvot: R. Bava Kamma 15a "Ish DeBar"
Procedure
Whether Kofer is paid based on the victim's worth or the aggressor's worth: Makkot 2b
Whether Kofer is paid for murder by an animal, as well as that performed by humans, or not: Bava Kamma 4a, 9b
Whether one pays Kofer at all, or perhaps halfway, for damage by a non-Dangerous Creature: Pesachim 22b, Bava Kamma 15a
Special Cases
Edim Zomimin who claimed that a man's animal killed a human being: Makkot 2b
