Murder is the unlawful killing of another human without justification or valid excuse, especially the unlawful killing of another human being with malice aforethought.[1][2][3] This state of mind may, depending upon the jurisdiction, distinguish murder from other forms of unlawful homicide, such as manslaughter. Manslaughter is a killing committed in the absence of malice, 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 (mens rea), recklessness.




Most societies consider murder to be a very serious crime, and thus believe that the person charged should receive harsh punishments for the purposes of retribution, deterrence, rehabilitation, or incapacitation. In most countries, a person convicted of murder generally faces a long-term prison sentence, possibly a life sentence where permitted.




In many common law jurisdictions, a person convicted of murder will receive a mandatory life sentence. In jurisdictions where capital punishment exists, the death penalty may be imposed for such an act; however, thiUnder state of mind (i), 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. In other words, "intent follows the bullet." 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 (iii), 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. An example of this is a 2007 law in California where an individual could be convicted of third-degree murder if he or she kills another person while driving under the influence of alcohol, drugs, or controlled substances. In Australian jurisdictions, the unreasonable risk must amount to a foreseen probability of death (or grievous bodily harm in most states), as opposed to possibility.[13]




Under state of mind (iv), 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.




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 offence. The jury might sympathise with the defendant (e.g. in a crime of passion, or in the case of a bullied victim who kills their tormentor), and the jury may wish to protect the defendant from a sentence of life imprisonment or execution.s practice is now less common.