Homicide is defined by the common law as the unjustified and unexcused killing of a human being. Most American jurisdictions in the nineteenth century divided homicide into two major categories, murder or manslaughter, and then subdivided these categories to reflect differences in available punishments. Murder was divided into first degree (for which a defendant could be executed) and second degree (which did not carry the death penalty). Manslaughter was viewed as a less serious killing and was not initially divided into degrees. However, over the years many states divided manslaughter into voluntary (or first degree) and involuntary (or second degree) manslaughter.
The Model Penal Code abolishes the “degrees” of murder, and makes all murders subject to the death penalty. The availability of the death penalty is a major, though unseen, factor in the development of homicide law. It is, indeed, the gorilla in the closet.