Actus Reus in Murder: Elements & Causation

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