Principles - actus reus

Introduction	In murder, the defendant causes the death of the victim. The result or consequence is the death. Therefore, some crimes are referred to as 'result' crimes. In these crimes, the offence specifies to the consequence. Another example is assault occasioning actual bodily harm. The causing of the harm is the consequence. In order to secure a conviction the prosecutor must prove that the defendant caused the result (caused the consequence).
Causation in fact
	To establish causation it is necessary to firstly ask if the defendant in fact caused of the specified consequence of the offence. One way is to ask "But for what the defendant did would the consequences have occurred?"
‘But For’ (or sine qua non) Test	"Sine qua non" is Latin for "without which, not" meaning an essential condition, something that is indispensable. In full it is "causa sine qua non" literally translated means cause without which - the event - could not have occurred. This is a basic and vital test for factual causation. If the result would not have occurred 'but for' what the defendant did, then the prosecution has established causation in fact. Unsurprisingly, this is referred to as the 'but for' test.
The prosecution failed to establish causation in fact in White (1910)	The defendant put cyanide into his mother's drink, but she died of heart failure before the poison could kill her. The answer to the question 'But for what the defendant did would she have died?' is 'No'. She would have died anyway. Not guilty of murder.
Other cases that illustrate the 'but for test' - and are also relevant to legal causation	R v Blaue (1975) Jehovah's Witness stabbed, refused blood transfusion. R v Jordan (1956) Stabbed, then given "palpably" wrong medical treatment. R v Cheshire (1991) Shot in chip shop, bad medical treatment. R v Dalloway (1847) driver of cart not holding reins, would have made no difference if he had.
Causation in law (sometimes called imputable causation)
Legal causation required in addition to factual	Having established causation in fact it is also necessary to establish causation in law. Causation in fact does not always mean there will be causation in law.
Operative or substantial cause, or intervening event reasonably foreseeable.	Causation in law can be established by showing that the defendant's act was an 'operative and substantial' cause of the consequence and that there was no intervening event. In R v Malcherek & Steel (two separate cases involving victims who where kept alive on life support machines that were switched off. The original injuries were held to be an operating and substantial cause. R v Smith (1959) (soldier stabbed in barracks)
'Substantial'	Means more than something very trivial, more than something that the law considers de minimis. Contrast a deep cut and a pin prick (both constitute wounds).
‘Operative’	An 'operative' cause does not have to be the ‘sole or main’ cause of the specified consequence Benge (1865). R v Dalloway (1847) (Carter not holding reins killed child)
Intervening events; novus actus interveniens
If merely a setting, chain would be broken.	If the defendant's act merely provided the setting in which some other cause operated the chain of causation would be broken Smith (1959).
Legal causation exists if result reasonably foreseeable.	Another way to show that defendant's act was the 'operative and substantial' cause in law is to ask if the result was a reasonably foreseeable consequence the defendant's actus.
Pagett (1983)	The defendant found guilty of causing the death of a girl. He held the girl hostage in front of him when he fired at armed police officers.
The 'thin skull' rule	The 'thin skull' rule says that the defendant must take his victim as he finds him. Therefore, even if injury or death is not reasonably foreseeable the law still considers the defendant liable if the victim suffered from some physical or mental condition that made him or her vulnerable.
..or egg shell skull rule.	It is called the 'thin skull rule' in appreciation that if you knock a person to the ground who has such a skull, the defendant should be liable. It is not the victim's fault that he was not blessed with a more substantial cranium.
Blaue (1975)	The defendant caused the death of a Jehovah's Witness whom he had stabbed.
Self-neglect	Victims sometimes neglect their wounds, or others neglect them. This may not be reasonably foreseeable even so such neglect will not break the chain of causation In a case quoted in the Scottish Law Commission report is California v Lewis where the victim having been shot cut his own throat rather than die slowly from the gunshot wounds.
Smith (1959)	Three soldiers engaged in a fight in their barracks, one was stabbed with a bayonet. He was carried by another soldier who dropped him twice on the way to the medical station.
Death caused by medical treatment
As a matter of policy seldom successful plea.	An original assailant can not escape liability by showing that his victim received inadequate, or negligent medical treatment, unless medical treatment is grossly negligent, Smith (1959)
When the medical treatment is grossly negligent, the chain of causation may be broken.	Jordan (1956) D stabbed V, who died eight days later in hospital. The medical treatment was 'palpably wrong'. R v Cheshire (1991) Shot in chip shop, bad medical treatment, but not 'papably wrong'.
Double Effect	The administration of pain easing drugs that incidentally shorten life by a very short period (hours or days, but not weeks or months) Would not amount to a cause in law of death Adams (1957). No doctor has ever been convicted of murder in the UK in these circumstances. In any event, juries have been shown unwilling to convict, as Dr Moor was relieved to find out when he was acquitted on 11 May 1999.