Murder occurs when one human being unlawfully kills another human being. See Homicide. The precise legal definition of murder varies by jurisdiction. Most states distinguish between different degrees of murder. Some other states base their murder laws on the Model Penal Code.
At common law, murder was defined as killing another human being with malice aforethought. Malice aforethought is a legal term of art, that encompasses the following types of murder:
- "Intent-to-kill murder"
- "Grievous-bodily-harm murder" - Killing someone in an attack intended to cause them grievous bodiliy harm. For example, if a person fatally stabbed someone, even if she only intended to wound her victim, she could still be executed.
- "Felony-murder" - Killing someone while in the process of committing a felony. Note that at common law, there were few felonies, and all carried the death penalty. For example, at common law, robbery was a felony. So if a robber accidentally killed someone during a robbery, the robber could be executed.
- "Depraved heart murder" - Killing someone in a way that demonstrates a callous disregard for the value of human life. For example, if a person intentionally fires a gun into a crowded room, and someone dies, the person could be convicted of depraved heart murder.
These definitions are valuable because they inform subsequent reforms of American murder law.
The Pennsylvania Method is a catch-all term for systems of classifying murder by degree. Certain, specified types of murder were first-degree murder, and carried the death penalty. All other types of murder were second-degree murder, which did not carry the death penalty.
First-Degree Murder includes:
- Willful, deliberate, and premeditated murder.
- Particularly heinous types of murder. For example, in the original Pennsylvania statute, this included poisoning and lying in wait to kill someone by ambush.
- Felony-murder, but only for certain listed felonies. For example, in the original Pennsylvania statute, the only eligible felonies were arson, rape, robbery, and burglary.
At present, most states either use the Pennsylvania Method or a similar method to categorize murder.
The Model Penal Code moved away from the traditional common law approach to murder. Under the Model Penal Code, the following constitute murder:
- Purposefully or knowingly killing another human being. This functions much the same as the common law rule against intentional murder.
- Killing another human being in circumstances showing extreme recklessness. This functions much the same as the common law's depraved heart murder rule.
- Felony-murder. The Model Penal Code disfavors but does not eliminate applying the death penalty for killings that occur during the commission of a felony. Instead of framing the rule as a felony-murder rule, it creates a rebuttable presumption that killings that occur during the commisison of listed dangerous felonies show extreme recklessness for purposes of the code's other murder provisions.