The law of murder is set out in common law. The legal definition of murder is 'the unlawful killing of a human being in the Queen's peace, with malice aforethought'.
The actus reus of murder consists of the unlawful killing of a human being in the Queen's peace. The mens rea of murder is malice aforethought, which has been interpreted by the courts as meaning intention to kill or intention to cause GBH.
A murder conviction carries a mandatory life sentence. The judge passing sentence can not pass a lesser sentence no matter how mitigating the circumstances might be. There exist three partial defences to murder which may reduce the conviction to voluntary manslaughter which carries a maximum sentence of life and thus allows the judge discretion on sentencing. These partial defences are contained in the Homicide Act 1957 and consist of diminished responsibility, provocation and suicide pact.
The actus reus of murder
The actus reus of murder is the unlawful killing of a human being in the Queen's peace.
Unlawful killing can be committed by an act or an omission. Therefore the case law relating to omissions found here will also be relevant to the law of murder. All unlawful killings are result crimes and thus causation must also be established.
Some killings may be classed as lawful. For example, killing in self-defence. Also when the death penalty was implemented, such state ordered executions would be classed as lawful. Soldiers and police may kill in the course of their duties but will be liable for murder if they go beyond their duty or use excessive force:
R v Clegg  1 AC 482 Case summary
Also doctors may lawfully kill in limited circumstances:
Administering pain relief see:
Dr Bodkin Adams 1957 Case summary
Withdrawal of treatment see:
Airedale Hospital Trustees v Bland  2 WLR 316 Case summary
The defence of necessity:
Re A  2 WLR 480 Case summary
The second element of the actus reus of murder requires the victim to be a human being. This obviously excludes animals from the remit of murder but raises questions as to at what point does one become a human being and at what point does one cease to be a human being.
A foetus is not classed as a human being and therefore a person who kills a foetus can not be charged with murder:
A-G ref (No 3 of 1994)  AC 245 Case summary
A foetus becomes a human being when it has been fully expelled from it mother and has an independent existence.
A person ceases to be a human being when their brain stem ceases to be active irrespective of whether they are being kept alive by artificial means:
R v Malcherek and Steel  2 ALL ER Case summary
R v Inglis  1 WLR 1110 Case summary
Disability now matter how extreme does not prevent a person being a human being see R v Inglis above.
In the Queen's Peace
The third aspect of the actus reus of murder excludes the killing of alien enemies in the time of war.
Mens rea of murder
The mens rea of murder is malice aforethought. However this term is misleading in that it suggests some sort of ill will and pre-planning. Malice aforethought has been interpreted in the courts as meaning intention to kill and intention to cause GBH.
R v Vickers  2 QB 664 Case summary
R v Cunningham  AC 566 Case summary
The mens rea of murder covers not only direct intent, but also extends to oblique intent where the current test established in R v Woollin (case summary)applies. See further the lecture on intention.
Law Commission Report - Murder, Manslaughter and infanticide