Murder

Murder is the unlawful killing of another human without justification or valid excuse committed with the necessary intention as defined by the law in a specific jurisdiction. This state of mind may, depending upon the jurisdiction, distinguish murder from other forms of unlawful homicide, such as manslaughter. Manslaughter is killing committed in the absence of malice, such as in the case of voluntary manslaughter brought about by reasonable provocation, or diminished capacity. Involuntary manslaughter, where it is recognized, is a killing that lacks all but the most attenuated guilty intent, recklessness.
Most societies consider murder to be an extremely serious crime, and thus believe that a person convicted of murder should receive harsh punishments for the purposes of retribution, deterrence, rehabilitation, or incapacitation. In most countries, a person convicted of murder generally receives a long-term prison sentence, a life sentence, or capital punishment. Some countries, states, and territories, including the United Kingdom and other countries with English-derived common law, mandate life imprisonment for murder, whether it is subdivided into first-degree murder or otherwise.

Etymology

The modern English word "murder" descends from the Proto-Indo-European *mŕ̥-trom which meant "killing", a noun derived from *mer- "to die".
Proto-Germanic, in fact, had two nouns derived from this word, later merging into the modern English noun: *murþrą "death, killing, murder", whence Old English morðor "secret or unlawful killing of a person, murder; mortal sin, crime; punishment, torment, misery"; and *murþrijô "murderer; homicide", giving Old English myrþra "homicide, murder; murderer". There was a third word for "murder" in Proto-Germanic, continuing Proto-Indo-European *mr̥tós "dead", giving Proto-Germanic *murþą "death, killing, murder" and Old English morþ "death, crime, murder".
The -d- first attested in Middle English mordre, mourdre, murder, murdre could have been influenced by Old French murdre, itself derived from the Germanic noun via Frankish *murþra, though the same sound development can be seen with burden. The alternative murther springs directly from the Old English forms. Middle English mordre is a verb from Anglo-Saxon myrðrian from Proto-Germanic *murþrijaną, or, according to the Oxford English Dictionary, from the noun.

Definition

The eighteenth-century English jurist William Blackstone, in his Commentaries on the Laws of England set out the common law definition of murder, which by this definition occurs
At common law, murder was normally punishable by death.
The elements of common law murder are:

unlawful : This distinguishes murder from killings that are done within the boundaries of law, such as capital punishment, justified self-defense, or the killing of enemy combatants by lawful combatants as well as causing collateral damage to non-combatants during a war.
killing : At common law life ended with cardiopulmonary arrest – the total and irreversible cessation of blood circulation and respiration. With advances in medical technology courts have adopted irreversible cessation of all brain function as marking the end of life.
through criminal act or omission : Killing can be committed by an act or an omission.
of a human : This element presents the issue of when life begins. At common law, a fetus was not a human being. Life began when the fetus passed through the vagina and took its first breath.
by another human : In early common law, suicide was considered murder. The requirement that the person killed be someone other than the perpetrator excluded suicide from the definition of murder.
with malice aforethought: Originally malice aforethought carried its everyday meaning – a deliberate and premeditated killing of another motivated by ill will. Murder necessarily required that an appreciable time pass between the formation and execution of the intent to kill. The courts broadened the scope of murder by eliminating the requirement of actual premeditation and deliberation as well as true malice. All that was required for malice aforethought to exist is that the perpetrator act with one of the four states of mind that constitutes "malice".

In contrast with manslaughter, murder requires the mental element known as malice aforethought. Mitigating factors that weigh against a finding of intent to kill, such as "loss of control" or "diminished responsibility", may result in the reduction of a murder charge to voluntary manslaughter.
The four states of mind recognized as constituting "malice" are:
Under state of mind, intent to kill, the deadly weapon rule applies. Thus, if the defendant intentionally uses a deadly weapon or instrument against the victim, such use authorizes a permissive inference of intent to kill. Examples of deadly weapons and instruments include but are not limited to guns, knives, deadly toxins or chemicals or gases and even vehicles when intentionally used to harm one or more victims.
Under state of mind, an "abandoned and malignant heart", the killing must result from the defendant's conduct involving a reckless indifference to human life and a conscious disregard of an unreasonable risk of death or serious bodily injury. In Australian jurisdictions, the unreasonable risk must amount to a foreseen probability of death, as opposed to possibility.
Under state of mind, the felony-murder doctrine, the felony committed must be an inherently dangerous felony, such as burglary, arson, rape, robbery or kidnapping. Importantly, the underlying felony cannot be a lesser included offense such as assault, otherwise all criminal homicides would be murder as all are felonies.
In Spanish criminal law, asesinato : takes place when any of these requirements concur: Treachery, price or reward or viciousness. After the last reform of the Spanish Criminal Code, in force since July 1, 2015, another circumstance that turns homicide into assassination is the desire to facilitate the commission of another crime or to prevent it from being discovered.
As with most legal terms, the precise definition of murder varies between jurisdictions and is usually codified in some form of legislation. Even when the legal distinction between murder and manslaughter is clear, it is not unknown for a jury to find a murder defendant guilty of the lesser offense. The jury might sympathize with the defendant, and the jury may wish to protect the defendant from a sentence of life imprisonment or execution.

Degrees

Some jurisdictions divide murder by degrees. The distinction between first- and second-degree murder exists, for example, in Canadian murder law and U.S. murder law. Some US states maintain the offense of capital murder.
The most common division is between first- and second-degree murder. Generally, second-degree murder is common law murder, and first-degree is an aggravated form. The aggravating factors of first-degree murder depend on the jurisdiction, but may include a specific intent to kill, premeditation, or deliberation. In some, murders committed by acts such as strangulation, poisoning, or lying in wait are also treated as first-degree murder. A few states in the U.S. further distinguish third-degree murder, but they differ significantly in which kinds of murders they classify as second-degree versus third-degree. For example, Minnesota and Pennsylvania define third-degree murder as depraved-heart murder, whereas Florida defines third-degree murder as felony murder.
Some jurisdictions also distinguish premeditated murder. This is the crime of wrongfully and intentionally causing the death of another human being after rationally considering the timing or method of doing so, in order to either increase the likelihood of success, or to evade detection or apprehension. State laws in the United States vary as to definitions of "premeditation". In some states, premeditation may be construed as taking place mere seconds before the murder. Premeditated murder is one of the most serious forms of homicide, and is punished more severely than manslaughter or other types of homicide, often with a life sentence without the possibility of parole, or in some countries, the death penalty. In the U.S., federal law criminalizes premeditated murder, felony murder and second-degree murder committed under situations where federal jurisdiction applies. In Canada, the criminal code classifies murder as either first- or second-degree. The former type of murder is often called premeditated murder, although premeditation is not the only way murder can be classified as first-degree. In the Netherlands, the traditional strict distinction between premeditated intentional killing and non-premeditated intentional killing is maintained; when differentiating between murder and manslaughter, the only relevant factor is the existence or not of premeditation. Manslaughter with aggravating factors is punished more severely, but it is not classified as murder, because murder is an offense which always requires premeditation.

Common law

According to Blackstone, English common law identified murder as a public wrong. According to common law, murder is considered to be malum in se, that is, an act which is evil within itself. An act such as murder is wrong or evil by its very nature, and it is the very nature of the act which does not require any specific detailing or definition in the law to consider murder a crime.
Some jurisdictions still take a common law view of murder. In such jurisdictions, what is considered to be murder is defined by precedent case law or previous decisions of the courts of law. However, although the common law is by nature flexible and adaptable, in the interests both of certainty and of securing convictions, most common law jurisdictions have codified their criminal law and now have statutory definitions of murder.