The killing must be an unlawful one. A killing which is unlawful, is one which cannot be excused or justified in law. This means that no defences exist which make the killing a lawful one.
For example, if a death occurs as a result of an act of self-defence which was proportionate in the circumstances, the law will not treat this as an unlawful killing. By contrast, if in the circumstances the force used was excessive, the law will treat this as an unlawful killing which can be tried as a murder, provided the other elements of the crime are satisfied.
The majority of cases in this area have dealt with two issues:
1 – Whether the actions of law enforcement authorities, such as the police and military, are no longer justified due to an excessive use of force.
2 – Whether medical professionals are entitled to remove life-sustaining treatment, such as artificial feeding and ventilation, from their patients, without this amounting to an unlawful killing.
Each of these areas will be explored in the cases below:
The first case explores the circumstances in which the actions of the law enforcement authorities are no longer justified due to an excessive use of force, and whether this constitutes an unlawful killing.
R v Clegg 
A killing by a soldier on active service or a police officer during the course of their duty, will usually not be unlawful. This is due to the plea of self-defence. However, where the force used is excessive the killing can amount to murder.
The following cases required the Court to decide what acts or omissions by a medical professional, if any, constitute an unlawful killing. The Courts have been mindful to draw a robust line between the removal of life-sustaining treatment which is lawful and actively bringing about a patient’s death, which remains unlawful as a form of euthanasia.
Airedale NHS Trust v Bland 
It is not an unlawful killing for medical professionals to remove life-sustaining treatment in circumstances where the continuation of the treatment is not in the best interests of the individual concerned.
R v Cox 
In R v Cox, medical professionals were held to have unlawfully killed their patient because they did a positive act to bring about their death. This was different to Airedale NHS Trust v Bland, where the medical professionals were asking to omit to care for their patient, which is not an unlawful killing.
Re A (conjoined twins) 
There is a difference between medical treatment which has the primary purpose of killing a patient – which is unlawful – and medical treatment which has the incidental consequence of killing a patient – which is lawful.