[A] Common Law and Statutory Homicide At very early common law, "homicide" was defined as "the killing of a human being by a human being." This definition included suicide. However, modern law defines "homicide" as "the killing of a human being by another human being." Suicide, therefore, is no longer a form of homicide in most statutes. Homicide is divided into two crimes murder and manslaughter.
 "Human Being" - The common law and majority approaches define the beginning of life as birth for purposes of interpreting the criminal homicide law. A minority of states now treat a viable or, at times, even nonviable fetus as a human being under the homicide statute.
Regarding the end of human life, a majority of states, either by statute or judicial decision, have incorporated "brain death" in their definition of "death."
 "Murder" The common law definition of "murder" is "the killing of a human being by another human being with malice aforethought."
 "Manslaughter" Manslaughter is "an unlawful killing of a human being by another human being without malice aforethought."
 "Malice" As the term has developed, a person kills another acts with the requisite "malice" if he possesses any one of four states of mind:
|1.)||the intention to kill a human being;|
|2.)||the intention to inflict grievous bodily injury on another;|
|3.)||an extremely reckless disregard for the value of human life; or|
|4.)||the intention to commit a felony during the commission or attempted commission of which a death results.|
[B] Model Penal Code A person is guilty of criminal homicide under the Model Code if he unjustifiably and inexcusably takes the life of another human being [MPC § 210.0(1)] purposely, knowingly, recklessly, or negligently. [MPC § 210.1(1)] The Code recognizes three forms of criminal homicide: murder, manslaughter, and (unlike the common law) negligent homicide.
[A] Degrees of Murder At common law, there were no degrees of murder, and murder was a capital offense. Reform of the common law has resulted in the division of murder into degrees, with only murder in the first degree being a capital offense.
The Model Penal Code rejects the degrees-of-murder approach.
[B] Intent to Kill
 "Deliberate and Premeditated" Typically, a murder involving the specific intent to kill is first-degree murder in jurisdictions that grade the offense by degrees if the homicide was also "deliberate" and "premeditated."
 "Wilful, Deliberate, Premeditated" Nearly all states that grade murder by degrees provide that a "wilful, deliberate, premeditated" killing is murder in the first degree.
 "Intent to Inflict Grievous Bodily Injury" Malice aforethought is implied if a person intends to cause grievous bodily injury to another, but death results. In states that grade murder by degree, this form of malice nearly always constitutes second-degree murder.
 Extreme Recklessness ("Depraved Heart" Murder) Malice aforethought is implied if a persons conduct manifests an extreme indifference to the value of human life. In states that separate murder into degrees, this type of murder almost always constitutes second-degree murder.
[C] Model Penal Code A homicide is murder if the defendant intentionally takes a life, or if he acts with extreme recklessness (i.e., depraved heart murder).
[A] Common Law At common law, a person is guilty of murder if he kills another person during the commission or attempted commission of any felony. Nearly every state retains the felony-murder rule.
[B] Statutory Law Under most modern murder statutes, a death that results from the commission of an enumerated felony (usually a dangerous felony, such as arson, rape, robbery, or burglary) constitutes first-degree murder for which the maximum penalty is death or life imprisonment. If a death results from the commission of an unspecified felony, it is second-degree murder. The felony-murder rule authorizes strict liability for a death that results from commission of a felony.
[C] Model Penal Code The Code also provides for felony-murder by setting forth that extreme recklessness (and, thus, murder) is presumed if the homicide occurs while the defendant is engaged in, or is an accomplice in, the commission, attempted commission, or flight from one of the dangerous felonies specified in the statute. [MPC § 210.2(1)(b)]
[A] Inherently-Dangerous-Felony Limitation Many states limit the rule to homicides that occur during the commission of felonies which by their nature are dangerous to human life, e.g., armed robbery.
[B] Independent Felony (or Merger) Limitation Most states recognize some form of "independent felony" or "collateral felony" limitation. That is, the felony-murder rule only applies if the predicate felony is independent of, or collateral to, the homicide. If the felony is not independent, then the felony merges with the homicide and cannot serve as the basis for a felony-murder conviction. For example, most jurisdictions hold that felonious assault may not serve as the basis for felony-murder.
[C] Res Gestae Requirement A requirement of the felony-murder rule is that the homicide must occur "within the res gestae [things done to commit] of the felony," which requires both:
|1.)||temporal and geographical proximity There must be a close proximity in terms of time and distance between the felony and the homicide. The res gestae period begins when the defendant has reached the point at which he could be prosecuted for an attempt to commit the felony, and it continues at least until all of the elements of the crime are completed. Most courts provide that the res gestae of a felony continues, even after commission of the crime, until the felon reaches a place of temporary safety.|
|2.)||A causal relationship between the felony and the homicide.|
[D] Killing by a Non-Felon
 The "Agency" Approach A majority of states that have considered the issue apply the so-called "agency" theory of felony murder, which precludes any killing committed during the commission of the felon by a person other that the defendant or his accomplices from serving as the basis for felony-murder. However, a killing by an accomplice can be imputed to others involved in the commission of the felony so that felony-murder can be charged against the non-killers.
 "Proximate Causation" Approach A minority of courts apply the "proximate causation" theory of felony-murder under which a felon is liable for any death proximately resulting from the felony, whether the killer is a felon or a third party.
 "Provocative Act" Doctrine A felon may be held responsible for the death of another at the hands of a third party, if the basis for the charge is not felony-murder, but instead is founded on what is sometimes termed the "provocative act" doctrine, which is simply a form of reckless homicide, e.g., a felon recklessly provokes a victim to shoot in self-defense, killing an innocent bystander.
[A] Forms of Manslaughter Traditionally, three types of unlawful killings constitute manslaughter:
|1.)||an intentional killing committed in "sudden heat of passion" as the result of "adequate provocation" (voluntary manslaughter);|
|2.)||an unintentional killing resulting from the commission of a lawful act done in an unlawful manner (involuntary manslaughter). This is akin to criminally negligent homicide.|
|3.)||an unintentional killing that occurs during the commission or attempted commission of an unlawful act (involuntary manslaughter). This type of manslaughter is sometimes dubbed "unlawful-act manslaughter," or if the killing occurred during the commission of a non-felony, "misdemeanor-manslaughter."|
[B] Provocation ("Sudden Heat of Passion")
 Elements of the Mitigating Factor Under common law principles, an intentional homicide committed in "sudden heat of passion" as the result of "adequate provocation" mitigates the offense to voluntary manslaughter. The common law defense contains four elements:
|1.)||The defendant must have acted in heat of passion at the moment of the homicide. "Passion" has been interpreted to include any violent or intense emotion such as fear, jealousy, and desperation.|
|2.)||The passion must have been the result of adequate provocation. Under the modern approach, it is up to the jury to determine what constitutes adequate provocation. Juries in such cases are typically instructed to apply an objective "reasonable-person" standard.|
|3.)||The defendant must not have had a reasonable opportunity to cool off.|
|4.)||There must be a causal link between the provocation, the passion, and the homicide.|
 Words as Adequate Provocation Surviving from the common law in most non-Model Penal Code jurisdictions is the rule that words alone do not constitute adequate provocation. However, a few courts allow the defense to be raised in the case of informational, but not insulting, words. Other courts have held open the possibility that insulting words may qualify in extreme circumstances. The "words alone" rule does not apply in jurisdictions following the Model Penal Code.
[C] Unlawful-Act (Misdemeanor-Manslaughter) An accidental homicide that occurs during the commission of an unlawful act not amounting to a felony (or, at least, not amounting to felony that would trigger the felony-murder rule) constitutes involuntary manslaughter. This may be termed "misdemeanor-manslaughter" or "unlawful-act manslaughter."
The scope of the doctrine varies widely by jurisdiction. Some courts limit its applicability to inherently dangerous misdemeanors while others apply the doctrine to all misdemeanors.
[D] Model Penal Code
 In General A person is guilty of manslaughter if he:
|1.)||recklessly kills another; or|
|2.)||kills another person under circumstances that would ordinarily constitute murder, but which homicide is committed as the result of "extreme mental or emotional disturbance" for which there is a "reasonable explanation or excuse."|
[MPC § 210.3(1)(a)-(b)]
The Code does not recognize any form of criminal homicide based on the unlawful-act (misdemeanor-manslaughter) rule. [MPC § 6.06(2).]
 Reckless and Criminally Negligent Homicide A person who kills another recklessly is guilty of manslaughter. In a sharp departure from the common law, the Code precludes liability for manslaughter based on criminal negligence. A criminally negligent homicide involuntary manslaughter at common law constitutes the lesser offense of negligent homicide under the Code. [MPC § 210.4]
 Extreme Mental or Emotional Disturbance A person who would be guilty of murder because he purposely or knowingly took a human life, or because he killed a person recklessly under circumstances manifesting an extreme indifference to the value of human life, is guilty of the lesser offense of manslaughter if he killed the victim while suffering from an "extreme mental or emotional disturbance" (EMED) for which there is "reasonable explanation or excuse." The reasonableness of the explanation or excuse regarding the EMED is "determined from the viewpoint of a person in the defendants situation under the circumstances as he believes them to be." The concept of EMED is intended to incorporate two common law doctrines: (1) sudden heat of passion (but in a much expanded form); and (2) partial responsibility (diminished capacity).
The EMED manslaughter provision is broader than the common law provocation defense in the following ways:
|1.)||a specific provocative act is not required to trigger the EMED defense;|
|2.)||even if there is a provocation, it need not involve "an injury, affront, or other provocative act perpetrated upon [the defendant] by the decedent";|
|3.)||even if the decedent provoked the incident, it need not fall within any fixed category of provocations;|
|4.)||words alone can warrant a manslaughter instruction;|
|5.)||there is no rigid cooling-off rule. The suddenness requirement of the common law that the homicide must follow almost immediately after the provocation is absent from the EMED defense.|