## Introduction

Actus reus is the physical element of a crime. In murder, it means the unlawful killing of a human being under the King’s peace. To prove it, the prosecution must show the conduct caused death in fact and in law, that the victim was a human being, that the killing was not legally justified, and that the conduct was voluntary unless a recognised exception applies. Liability can also arise from failing to act where a legal duty exists.

This guide explains the elements, how causation works, when omissions can suffice, and where voluntariness matters, with clear examples and practical pointers.

## What You’ll Learn

- The four parts of the actus reus of murder: killing, unlawfulness, a human being, and under the King’s peace
- How factual causation (the ‘but for’ test) and legal causation (a significant and operating cause) work
- When the chain of causation is broken by third parties, the victim’s own response, medical treatment, or natural events
- The thin skull rule and the single transaction principle from Thabo Meli
- When omissions can amount to murder or manslaughter, and the main sources of a duty to act
- Voluntariness, automatism, and rare “state of affairs” offences
- How voluntary intoxication interacts with specific and basic intent offences
- A step-by-step approach to problem questions and case analysis

## Core Concepts

### The elements of the actus reus of murder

To establish the actus reus of murder, the prosecution must prove:

- A killing
  - Death must result from the defendant’s conduct. The conduct can be a positive act or, in limited circumstances, an omission where a legal duty exists.
  - Death is determined by current medical standards. Brain-stem death is treated as death: see Malcherek and Steel.
- Unlawfulness
  - The killing must not be justified or excused. Lawful killings include self-defence or defence of others where reasonable force is used (common law and section 3 Criminal Law Act 1967).
- A human being
  - The victim must be a “reasonable creature in rerum natura”. A foetus is not a person until born alive (Attorney General’s Reference (No 3 of 1994)).
- Under the King’s peace
  - Excludes killings of enemy combatants in recognised armed conflict.
- Note: The old “year and a day” rule has been abolished by statute.

### Causation: factual and legal tests

Causation links conduct and consequence.

- Factual causation: the ‘but for’ test
  - Ask: but for the defendant’s conduct, would the victim have died when and as they did? If yes, factual causation fails. In R v White (1910), the mother died of heart failure despite poison in her drink, so the poison was not a factual cause.

- Legal causation: a significant and operating cause
  - The conduct must be more than minimal (not de minimis) and be an operating cause at the time of death. In R v Smith (1959), the stabbing remained a substantial cause despite poor treatment and the victim being dropped en route to care.
  - Medical treatment
    - Only extraordinary treatment that is “so independent” and “potent” may break the chain (R v Jordan (1956) is exceptional). Usually, negligent treatment does not break it (R v Cheshire (1991)).
  - Third-party acts and self-defence
    - A free, deliberate, informed act may break the chain, but reasonable acts in self-defence do not (R v Pagett (1983)).
  - The victim’s response
    - The chain remains intact if the victim’s reaction was reasonably foreseeable (R v Roberts (1971)). It may break if the response was so “daft” or unexpected that it could not reasonably be foreseen (R v Williams & Davis (1992)).
  - Thin skull rule
    - Take the victim as you find them, including physical or religious vulnerabilities (R v Blaue (1975)).
  - Natural events
    - Only a truly unforeseeable act of nature will break the chain.
  - Single transaction principle
    - Where a series of acts forms one plan, coincidence of actus reus and mens rea can be satisfied across the sequence (R v Thabo Meli (1954)).

### Omissions and duties to act

Criminal liability usually rests on positive acts. Omissions can suffice when there is a legal duty to act and a breach causes death. Key duty sources include:

- Contractual duties: R v Pittwood (1902) – a gatekeeper’s failure to close a railway crossing led to death.
- Special relationships: R v Gibbins and Proctor (1918) – a parent (and partner who assumed the role) starved a child to death; murder by omission was established.
- Voluntary assumption of care: R v Stone and Dobinson (1977) – failure to care for a dependent relative led to manslaughter.
- Creating a dangerous situation: R v Miller (1983) – starting a fire created a duty to take steps to avert the danger; failure to do so attracted liability. Also see R v Evans (2009) on supplying heroin and creating a foreseeable risk requiring intervention.
- Public office: R v Dytham (1979) – wilful neglect of duty by a police officer.

For murder by omission, the duty must be clear, causation must be proved, and the mental element for murder must be present.

### Voluntariness, automatism, and state of affairs

- Voluntary conduct
  - Liability for actus reus generally requires a voluntary act. Where actions are truly involuntary, criminal responsibility may not follow.
- Automatism
  - In R v Quick (1973), hypoglycaemia (triggered by insulin) was an external cause; automatism could apply. Contrast with R v Hennessy (1989), where hyperglycaemia from diabetes was internal and fell within insanity rules.
- External compulsion
  - In Leicester v Pearson (1952), the driver’s car was shunted onto a crossing; the lack of voluntary control led to acquittal.
- State of affairs offences (rare)
  - Liability may arise from being in a proscribed state even without voluntary entry into it: R v Larsonneur (1933) and Winzar v Chief Constable of Kent (1983). These are exceptional and controversial; they are not the usual route to murder liability.

### Intent categories and their practical effect

Although intent is part of mens rea, it can affect how the actus reus is treated in analysis:

- Specific intent vs basic intent
  - Specific intent crimes require intent that goes beyond the act itself (R v Heard (2007)); murder is a specific intent crime.
  - Voluntary intoxication can prevent formation of specific intent (reducing murder to manslaughter), but it does not excuse the conduct. For basic intent offences, intoxication usually provides no defence (DPP v Majewski (1977)).
- Accomplices
  - Where an accessory assists or encourages, liability turns on what was contemplated and intended. R v Gilmour (NICA 2000) shows an accessory is not liable for consequences beyond what they foresaw; this is primarily a mens rea point, but remember the actus reus remains the causing of death by the principal conduct.

## Key Examples or Case Studies

- R v White (1910)
  - Poisoned drink; death actually due to heart failure. Factual causation failed; no murder.

- R v Smith (1959)
  - Stabbing remained a substantial and operating cause despite poor treatment and being dropped. Legal causation satisfied.

- R v Cheshire (1991) and R v Jordan (1956)
  - Cheshire: negligent treatment rarely breaks the chain. Jordan: only truly extraordinary treatment will do so; a rare exception.

- R v Pagett (1983)
  - Using a pregnant woman as a shield; police return fire in self-defence did not break the chain. The defendant’s conduct remained the legal cause.

- R v Blaue (1975)
  - Victim refused a life-saving transfusion on religious grounds. Thin skull rule applied; the refusal did not break the chain.

- R v Roberts (1971) and R v Williams & Davis (1992)
  - Victim’s escape from sexual advances (Roberts) was foreseeable; chain intact. Where a victim’s reaction is grossly disproportionate and unforeseeable, the chain may break (Williams & Davis).

- R v Thabo Meli (1954)
  - A series of acts treated as one transaction; coincidence between actus reus and mens rea established across the sequence.

- R v Gibbins and Proctor (1918)
  - Murder by omission based on parental duty and assumed responsibility; starvation causing death.

- R v Miller (1983) and R v Evans (2009)
  - Creating a dangerous situation creates a duty to act. Failure to take reasonable steps can found liability.

- R v Quick (1973) and R v Hennessy (1989)
  - Automatism vs insanity depending on whether the cause is external (Quick) or internal (Hennessy).

- Leicester v Pearson (1952); Larsonneur (1933); Winzar (1983)
  - Examples of involuntariness and rare state-of-affairs liability.

- R v Gilmour (NICA 2000)
  - Accessorial liability limited by what was contemplated; relevant to mens rea, but commonly discussed with actus reus problems involving group actions.

## Practical Applications

- Map the elements
  - Confirm death, identify the conduct said to have caused it, and check that the victim was a human being and the killing was under the King’s peace.
  - Consider any lawful justification (self-defence, prevention of crime).

- Run causation step by step
  - Factual: Apply the ‘but for’ test.
  - Legal: Ask whether the conduct remained a significant and operating cause. Consider:
    - Medical treatment: ordinary negligence usually does not break the chain (Cheshire); only exceptional treatment does (Jordan).
    - Third parties: were their acts free, deliberate, and informed? If acting reasonably in self-defence (Pagett), the chain typically holds.
    - Victim’s acts: were they a foreseeable response (Roberts) or so unexpected they break the chain (Williams & Davis)?
    - Thin skull: apply Blaue; do not discount vulnerabilities or beliefs.
    - Natural events: only the extraordinary will break the chain.

- Check for omissions
  - Identify duties: contract (Pittwood), relationship (Gibbins & Proctor), assumption of care (Stone and Dobinson), creation of danger (Miller; Evans), public office (Dytham).
  - Prove breach, causation, and, for murder, the required mental element.

- Test voluntariness
  - Was the act willed? Consider automatism (Quick) and involuntary movement (Leicester v Pearson). If the cause is internal (Hennessy), insanity rules may apply.

- Address timing and series of acts
  - Where acts form one plan, use Thabo Meli to deal with coincidence of actus reus and mens rea.

- Deal with intoxication carefully
  - Murder is a specific intent offence. If voluntary intoxication prevents intent, consider manslaughter. The actus reus (killing) remains; the issue is mens rea.

- Evidence and case preparation
  - Obtain clear medical evidence on cause of death and timing.
  - Record all intervening acts and the victim’s condition.
  - Take statements on the foreseeability of the victim’s reactions.
  - For omissions, gather proof of the duty and its scope (contracts, family links, steps taken or not taken).
  - Anticipate defence points on self-defence, automatism, or chain-breaking events.

- Exam technique
  - Use a structured approach: elements → factual causation → legal causation → chain-breaking → omissions → voluntariness → timing (Thabo Meli) → intoxication (where relevant).
  - Cite key authorities concisely to support each step.

## Summary Checklist

- Unlawful killing of a human being under the King’s peace shown
- Factual causation: ‘but for’ test satisfied (White)
- Legal causation: conduct is a significant and operating cause (Smith; Cheshire)
- No break in the chain by third parties, victim, medical treatment, or natural events
- Thin skull rule considered (Blaue)
- Any omission supported by a clear duty and breach (Pittwood; Gibbins & Proctor; Miller)
- Voluntariness assessed; automatism or involuntariness ruled in or out (Quick; Leicester v Pearson)
- Timing issues addressed with single transaction principle if needed (Thabo Meli)
- Intoxication analysed for mens rea consequences (Heard; Majewski)
- Any lawful justification (self-defence) considered and evidenced

## Quick Reference

| Concept               | Authority                                                | Key Takeaway                                           |
| --------------------- | -------------------------------------------------------- | ------------------------------------------------------ |
| Murder actus reus     | Common law                                               | Unlawful killing of a human under the King’s peace     |
| Factual causation     | R v White (1910)                                         | ‘But for’ the conduct, death would not have occurred   |
| Legal causation       | R v Smith (1959); R v Cheshire (1991)                    | Conduct must be a significant and operating cause      |
| Chain-breaking events | R v Pagett (1983); R v Roberts (1971)                    | Self-defence and reasonable escape keep the chain      |
| Thin skull rule       | R v Blaue (1975)                                         | Take the victim as you find them                       |
| Omissions and duties  | Pittwood (1902); Gibbins & Proctor (1918); Miller (1983) | Duties from contract, relationship, or creating danger |

Actus Reus in Murder: Elements & Causation