Murder can be generally defined as 1) the taking of life, 2) by conduct of the defendant 3) with a requisite mens rea and 4) an absence of justification. There must also be sufficient proof of death. This is sometimes referred to as the corpus delecti requirement.
Taking of Life
In order for murder to have occurred, a life must exist. Two factual scenarios arise in which this element is in question.
First, when an individual kills a foetus, has the taking of life occured? The answer to this question may depend on the jurisidiction in which the murder takes place. Early courts refused to recognize a foetus as a life. In response to these cases several states either broadened the definition of murder to include a foetus or created a separate crime of foetal homicide. Interestingly, the viability of the foetus may not even be an issue in some of these jurisdictions. In some cases, this issue has been dealt with as one of transferred intent.
Second, is the defendant responsible for murder if the person is already dead when the defendant's conduct occured. Death is generally defined by either lack of heartbeat or lack of brain activity. This may be an issue in simultaneous death where the sequence of death changes the lines of inheritance. It should be noted here that the shooting of a corpse cannot be murder. However it could potentially be attempted murder or even abuse of corpse in some jurisdictions.
Conduct of the Defendant
In order for the crime of murder to have occured, the defendant engage in some conduct or actus reus that causes the death. Such conduct can either be an affirmative act (firing a weapon) or an ommission (failure to provide food to kidnapping victim). The issue of whether the conduct is sufficiently connected to the death may arise in certain circumstances. For instance, if a doctor provides an individual with sleeping pills knowing that the individual intends to use them to commit suicide, are they liable for murder? Courts may differ, however several have stated that the defendant is not liable for murder on an assisted suicide theory. 
Mens Rea (Culpable Mental State) is also required in order for a defendant to be found guilty of murder. The following mental states may satisfy the mens rea requirement for murder. The exact definition of this mental state may vary from one jurisdiction to another.
- Malice Aforethought - Not a distinct mens rea, Malice Aforethought is commnon law legal concept that encompasses many different mental states including
- Intent to Kill
- Intent to do Serious Bodily Harm
- Depraved Heart Murder - The mens rea may be satisifed under this theory if the defendant acted in a way that demonstrated reckless indifference to human life.
- Felony Murder
Absence of Justification
The existence of an additional mental state or element may either mitigate or eliminate the existence of a crime. For instance, provocation on part of the victim may reduce the defandant's culpability from murder to voluntary manslaughter.
Literally, "Body of the Crime" in Latin, the Corpus Delecti does not require the production of a physical body as an element of proof that the crime of murder has been committed. Proof of death, like any other element of the crime, can be proven through circumstantial evidence.
Degrees of Murder
Murder is often divided into two or three degrees of murder. In some jurisdictions First Degree Murder occurs if the killing is premediated and delibrate.
Examples of Murder Statutes
Model Penal Code
The Model Penal Code offers a somewhat simplified version of the common law, dividing murder into three types: murder, manslaughter or negligent homicide.
(1) A person is guilty of criminal homicide if he purposely, knowingly, recklessly or negligently causes the death of another human being.
(2) Criminal homicide is murder, manslaughter or negligent homicide.
(1) Except as provided in Section 210.3(1)(b), criminal homicide constitutes murder when:
(a) it is committed purposely or knowingly; or
(b) it is committed recklessly under circumstances manifesting extreme indifference to the value of human life. Such recklessness and indifference are presumed if the actor is engaged or is an accomplice in the commission of, or an attempt to commit, or flight after committing or attempting to commit robbery, rape or deviate sexual intercourse by force or threat of force, arson, burglary, kidnaping or felonious escape.
(2) Murder is a felony of the first degree [but a person convicted of murder may be sentenced to death, as provided in Section 210.6].
(1) Criminal homicide constitutes manslaughter when:
(a) it is committed recklessly; or
(b) a homicide which would otherwise be murder is committed under the influence of extreme mental or emotional disturbance for which there is reasonable explanation or excuse. The reasonableness of such explanation or excuse shall be determined from the viewpoint of a person in the actor's situation under the circumstances as he believes them to be.
(2) Manslaughter is a felony of the second degree.
(1) Criminal homicide constitutes negligent homicide when it is committed negligently.
(2) Negligent homicide is a felony of the third degree.
(1) Causing Suicide as Criminal Homicide. A person may be convicted of criminal homicide for causing another to commit suicide only if he purposely causes such suicide by force, duress or deception.
(2) Aiding or Soliciting Suicide as an Independent Offense. A person who purposely aids or solicits another to commit suicide is guilty of a felony of the second degree if his conduct causes such suicide or an attempted suicide, and otherwise of a misdemeanor.
California Penal Code Sectiom 187:
(a)Murder is the unlawful killing of a human being, or a fetus, with malice aforethought.
(b)This section shall not apply to any person who commits an act that results in the death of a fetus if any of the following apply:
(1)The act complied with the Therapeutic Abortion Act, Article 2 (commencing with Section 123400) of Chapter 2 of Part 2 of Division 106 of the Health and Safety Code.
(2)The act was committed by a holder of a physician's and surgeon's certificate, as defined in the Business and Professions Code, in a case where, to a medical certainty, the result of childbirth would be death of the mother of the fetus or where her death from childbirth, although not medically certain, would be substantially certain or more likely than not.
(3)The act was solicited, aided, abetted, or consented to by the mother of the fetus.
(c)Subdivision (b) shall not be construed to prohibit the prosecution of any person under any other provision of law.
- Keeler v. Superior Court, 470 P.2d 617 (Cal. 1970) but see Commonwealth v. Cass, 467 N.E.2d 1324 (Mass. 1984)
- People v. Kevorkian, 527 N.W.2d 714 (Mich. 1994)