## Introduction

The actus reus of murder is the external element of the offence. In England and Wales it means causing the death of a human being, unlawfully, under the King’s peace. To convict, the prosecution must prove that the defendant’s conduct (an act or, in limited cases, an omission) caused the death in both a factual and legal sense.

This guide sets out the key elements, how causation is assessed, when a failure to act can count, and the requirement that the conduct be voluntary. It also clarifies the limits of doctrines such as transferred malice and includes leading cases you can cite with confidence.

## What You'll Learn

- What counts as an unlawful killing under the King’s peace
- How the law defines a “human being” and the start/end of life
- The tests for factual and legal causation and how the chain of causation can break
- When omissions can amount to the actus reus (duties to act)
- Why the act must be voluntary (automatism and “state of affairs” cases)
- How transferred malice works and where it stops
- Key cases: White, Smith, Kennedy (No 2), Pagett, Wallace, Pittwood, Stone & Dobinson, Miller
- A step-by-step method for tackling problem questions on murder actus reus

## Core Concepts

### Unlawful killing under the King’s peace

- Murder at common law requires an unlawful killing. Lawful killings include, for example, justified force in self-defence or defence of another where force is reasonable (Criminal Justice and Immigration Act 2008, s.76).
- “Under the King’s peace” excludes killing in lawful combat during war. It covers killings in ordinary circumstances within the jurisdiction.
- If a complete defence (such as self-defence) succeeds, the “unlawful” element fails and there is no murder.

### “Human being”: when life starts and ends

- The victim must be a living human being at the time of the act or omission. A foetus is not a “person” until it has an existence independent of the mother. See AG’s Reference (No 3 of 1994) [1998] AC 245.
- Death is assessed using modern medical criteria. In R v Malcherek; R v Steel [1981], brain-stem death counted as death; switching off a life support machine in those circumstances did not break causation.
- Withdrawal of life-sustaining treatment can be lawful where it is in the patient’s best interests and approved by the court (Airedale NHS Trust v Bland [1993]). This is treated as an omission and, if lawfully undertaken, does not amount to murder.

### Causation: factual and legal

- Factual causation uses the “but for” test: but for the defendant’s conduct, would the death have occurred? If yes, factual causation fails. R v White [1910] illustrates this: poison was administered, but death was due to an unrelated heart attack.
- Legal causation asks whether the defendant’s conduct was a substantial and operating cause of death. It need not be the sole or main cause. In R v Smith [1959], poor medical treatment did not displace the original wound as the operating and substantial cause.
- Intervening acts (novus actus interveniens) can break the chain:
  - A free, voluntary and informed act by the victim can do so. In R v Kennedy (No 2) [2007], a fully informed adult’s self-injection of heroin broke the chain from the supplier.
  - Reasonable acts of third parties in self-defence or in execution of duty usually do not break the chain. In R v Pagett (1983), police returning fire was a foreseeable response to the defendant’s conduct; causation remained with the defendant.
  - Medical treatment only breaks the chain if it is so independent and so potent in causing death that the original act becomes insignificant. Ordinary negligence is not enough; see R v Smith [1959].
- The thin skull rule applies: take your victim as you find them. A defendant remains liable even if the victim’s pre-existing condition contributes to death (R v Blaue [1975]).

### Omissions: when a failure to act suffices

Most crimes require an act, but the actus reus of homicide can be satisfied by an omission where a duty to act exists and the omission causes death. Duties arise where:

- There is a contractual duty: R v Pittwood [1902] (gatekeeper failed to close a railway crossing).
- There is a recognised relationship: parents owe duties to their children (see e.g., R v Gibbins & Proctor [1918]).
- A duty has been voluntarily assumed: R v Stone and Dobinson [1977] (assumed care of a relative and failed to provide adequate assistance).
- The defendant created a dangerous situation: R v Miller [1983] (duty to take reasonable steps to avert the danger one has created).
- A statute imposes a duty (various public safety provisions).

The omission must make a causal contribution to the death under the normal rules of factual and legal causation.

### Voluntariness and “state of affairs” offences

- The actus reus generally requires voluntary conduct. If the body moves without control (automatism due to an external factor), there may be no actus reus. In R v Quick [1973], hypoglycaemia caused by insulin was an external factor.
- By contrast, conditions caused by internal factors (often considered under insanity) are treated differently. Intoxication usually goes to mens rea rather than actus reus.
- “State of affairs” offences (e.g., being found “drunk on a highway” in Winzar v Chief Constable of Kent [1983]; presence contrary to conditions in R v Larsonneur [1933]) are strict in form and do not require a voluntary act at the moment of offence. Murder is not such an offence; it still requires conduct that causes death, subject to the limited omission duties above.

### Transferred malice (and its limits)

- If D intends to kill or cause serious harm to A but by mistake kills B, the mental element transfers to the actual victim (e.g., R v Latimer (1886) for unlawful act transfer between persons). The actus reus remains a killing of a human being caused by D.
- Transfer does not cross offence types (R v Pembliton (1874)): intent directed at property will not transfer to a crime against the person.
- Remember: transferred malice is about mens rea. For actus reus, you still need causation and an unlawful killing of a human being under the King’s peace.

## Key Examples or Case Studies

- R v White [1910] 2 KB 124
  - Facts: D poisoned his mother, who died of a heart attack unrelated to the poison.
  - Held: No factual causation for murder (“but for” test failed); D convicted of attempted murder.
  - Use: Start with “but for” analysis in every causation question.

- R v Smith [1959] 2 QB 35
  - Facts: Victim received poor medical treatment after being stabbed by D.
  - Held: Original wound remained the operating and substantial cause; causation not broken.
  - Use: Ordinary medical negligence rarely breaks the chain.

- R v Kennedy (No 2) [2007] UKHL 38
  - Facts: D supplied heroin; V self-injected and died.
  - Held: Fully informed and voluntary self-injection breaks the chain from the supplier.
  - Use: Look for informed autonomy in drug cases.

- R v Pagett (1983) 76 Cr App R 279
  - Facts: D used his girlfriend as a human shield while shooting; police returned fire and she died.
  - Held: Police actions were a reasonable response; D remained the legal cause of death.
  - Use: Third-party self-defence rarely constitutes a breaking act.

- R v Wallace [2018] EWCA Crim 690
  - Facts: V chose euthanasia abroad after catastrophic injuries from D’s acid attack.
  - Held: The euthanasia did not break the chain; the injuries were a substantial cause of death.
  - Use: Victim’s medical choices in response to grave injuries usually do not sever causation.

- R v Pittwood [1902] 19 TLR 37
  - Facts: Railway gatekeeper failed to lower gate; fatal collision occurred.
  - Held: Contractual duty; omission could ground liability.
  - Use: Identify duties from contracts impacting public safety.

- R v Stone and Dobinson [1977] QB 354
  - Facts: Defendants assumed care of an ailing relative but failed to secure help; she died.
  - Held: Assumption of responsibility created a duty; omission liable.
  - Use: Look for voluntary assumption of care and failure to act.

- R v Miller [1983] 2 AC 161
  - Facts: D accidentally started a fire and did nothing to extinguish it.
  - Held: Creating a dangerous situation imposes a duty to take reasonable steps to avert harm.
  - Use: If D creates the risk, a failure to mitigate can complete the actus reus.

## Practical Applications

- Structure your answer
  - Identify the elements: unlawful killing, human being, causation.
  - Check for a duty to act if the conduct is an omission.
  - Assess voluntariness before moving on to mens rea.

- Prove causation step by step
  - Factual causation: apply the “but for” test (White).
  - Legal causation: was D’s conduct a substantial and operating cause (Smith)?
  - Consider intervening acts: informed, voluntary acts by adults (Kennedy (No 2)); third-party self-defence (Pagett); medical treatment and its potency relative to the original injury (Smith).
  - Remember the thin skull rule (Blaue): do not discount the victim’s vulnerabilities.

- Deal with end-of-life issues
  - Brain-stem death counts as death; switching off life support in those circumstances does not break causation (Malcherek; Steel).
  - Lawful withdrawal of treatment (Bland) can be an omission and is not murder.

- Spot and apply omission duties
  - Contractual duty (Pittwood).
  - Special relationships (e.g., parent–child).
  - Assumption of responsibility (Stone & Dobinson).
  - Creation of danger (Miller).
  - Any statutory duty.

- Voluntariness
  - Consider automatism (external factor) and whether the act was under D’s control (Quick).
  - Distinguish “state of affairs” offences; murder still needs a causative act or qualifying omission.

- Transferred malice
  - If the wrong person is killed, the mental element may transfer between victims, but not between different offence types (Latimer; Pembliton).
  - Do not rely on transferred malice to fix causation problems; the actus reus must still be proved.

Tip: In problem questions, map the timeline. Pinpoint the initial act or omission, any subsequent events, and evaluate whether each later event was free, informed, and sufficiently independent to sever causation.

## Summary Checklist

- Unlawful killing of a human being under the King’s peace (common law)
- Victim status: living human being; start/end of life rules (AG’s Ref (No 3 of 1994); Malcherek; Steel; Bland)
- Factual causation: “but for” test (White)
- Legal causation: operating and substantial cause (Smith)
- Intervening acts: voluntary informed acts (Kennedy (No 2)); reasonable third-party responses (Pagett); medical treatment threshold (Smith)
- Thin skull rule applies (Blaue)
- Omissions liability: contractual, relationship, assumed responsibility, creation of danger, statutory (Pittwood; Stone & Dobinson; Miller)
- Voluntariness required; consider automatism and “state of affairs” limits (Quick; Larsonneur; Winzar)
- Transferred malice between victims, not across offence types (Latimer; Pembliton)

## Quick Reference

| Concept                        | Leading authority                  | Key point                                                     |
| ------------------------------ | ---------------------------------- | ------------------------------------------------------------- |
| Actus reus of murder           | Common law                         | Unlawful killing of a human being under the King’s peace      |
| Factual causation              | R v White [1910]                   | “But for” test must be satisfied                              |
| Legal causation                | R v Smith [1959]                   | Original act must be an operating and substantial cause       |
| Intervening act: victim choice | R v Kennedy (No 2) [2007]          | Informed, voluntary act can break the chain                   |
| Third-party response           | R v Pagett (1983)                  | Reasonable self-defence usually does not break the chain      |
| Omissions duties               | Pittwood; Stone & Dobinson; Miller | Duty to act may arise from contract, care, or creating danger |
| Voluntariness/automatism       | R v Quick [1973]                   | External factor may negate voluntary act                      |


Murder Actus Reus: Definition & Elements