Criminal Law Study Guide
Criminal Law examines the doctrines that define criminal offenses and the defenses available to accused persons. Unlike torts, which compensate victims for harm, criminal law focuses on punishment and deterrence imposed by the state. The course analyzes both the common law of crimes and the Model Penal Code (MPC), which has influenced the criminal codes of most American jurisdictions.
Every crime requires two fundamental elements: a voluntary act (actus reus) and a culpable mental state (mens rea). The actus reus can be an affirmative act, an omission (when there is a legal duty to act), or possession. Mens rea ranges from purpose (the highest level of culpability) through knowledge, recklessness, and negligence under the MPC framework. Understanding the distinction between specific intent and general intent at common law, and between the four MPC mental states, is essential for analyzing any criminal offense.
The bulk of the course covers specific crimes — primarily homicide (murder in its various degrees, voluntary and involuntary manslaughter) — and defenses (self-defense, insanity, necessity, duress, intoxication). Inchoate crimes (attempt, conspiracy, solicitation) address liability for criminal conduct that falls short of completion. Policy questions — why we punish, retribution vs. deterrence vs. rehabilitation, proportionality — run throughout.
Table of Contents
1Actus Reus & Mens Rea
The actus reus requirement ensures that criminal liability is based on conduct, not mere thoughts. The act must be voluntary — reflexive movements, acts during unconsciousness, and conduct under hypnosis generally do not qualify. Omissions can satisfy the actus reus only when the defendant had a legal duty to act (by statute, contract, relationship, voluntary assumption, or creation of the peril). Mens rea — the mental state accompanying the prohibited act — is the most heavily tested element. The MPC defines four levels: purpose, knowledge, recklessness, and negligence. Willful blindness (deliberate ignorance) can satisfy the knowledge requirement.
Key Doctrines
- Voluntary act requirement
- Omission liability (duty to act)
- MPC mental states (purpose, knowledge, recklessness, negligence)
- Specific intent vs. general intent (common law)
- Willful blindness / deliberate ignorance
- Strict liability offenses
- Transferred intent
- Mistake of fact
- Mistake of law
- Proof beyond a reasonable doubt (In re Winship)
2Homicide
Homicide is the most heavily tested criminal-law topic. At common law, murder is the unlawful killing of a human being with malice aforethought. Malice can be shown by intent to kill, intent to inflict grievous bodily harm, depraved-heart recklessness (extreme indifference to human life), or felony murder. First-degree murder typically requires premeditation and deliberation. Voluntary manslaughter is an intentional killing committed in the heat of passion upon adequate provocation. Involuntary manslaughter involves an unintentional killing through criminal negligence or during an unlawful act. The MPC simplifies the analysis by defining murder as purposeful, knowing, or extremely reckless killing, and manslaughter as reckless killing or killing under extreme emotional disturbance.
Key Doctrines
- Malice aforethought
- Premeditation and deliberation
- Intent-to-kill murder
- Depraved-heart murder
- Felony murder rule
- Voluntary manslaughter (heat of passion / provocation)
- Involuntary manslaughter (criminal negligence)
- MPC extreme emotional disturbance
- Year-and-a-day rule
- Causation in homicide (actual and proximate)
3Theft Offenses
Traditional theft offenses include larceny, embezzlement, false pretenses, robbery, and extortion. Larceny requires a trespassory taking and carrying away (asportation) of the personal property of another with the intent to permanently deprive. Embezzlement involves the fraudulent conversion of property by one in lawful possession. False pretenses requires obtaining title to property through a false representation of a material past or present fact. Many jurisdictions have consolidated these into a single theft statute. Robbery adds force or intimidation to larceny.
Key Doctrines
- Larceny (trespassory taking + asportation + intent to permanently deprive)
- Embezzlement (conversion by lawful possessor)
- False pretenses (obtaining title by misrepresentation)
- Larceny by trick
- Robbery (larceny + force or threat)
- Extortion / blackmail
- Consolidated theft statutes
- Continuing trespass doctrine
Essential Cases
4Inchoate Crimes: Attempt, Conspiracy & Solicitation
Inchoate crimes punish conduct that is directed toward but falls short of completing a target offense. Attempt requires the specific intent to commit the crime plus a substantial step toward its commission (MPC) or coming dangerously close to completion (common law). Conspiracy requires an agreement between two or more persons to commit a crime, plus (in most jurisdictions) an overt act in furtherance. Under Pinkerton liability, each conspirator is liable for the foreseeable crimes of co-conspirators in furtherance of the conspiracy. Solicitation requires asking, encouraging, or commanding another to commit a crime.
Key Doctrines
- Attempt (intent + substantial step / dangerous proximity)
- Impossibility (factual vs. legal)
- Abandonment / renunciation
- Conspiracy (agreement + overt act)
- Pinkerton liability
- Bilateral vs. unilateral conspiracy
- Wharton's Rule
- Solicitation
- Merger doctrine (attempt merges, conspiracy does not)
Essential Cases
5Defenses
Criminal defenses fall into two categories: justifications (the act was right or permissible under the circumstances) and excuses (the act was wrong but the actor is not morally blameworthy). Self-defense is the paradigmatic justification — a person may use reasonable force to defend against an imminent unlawful attack. Deadly force is justified only when the person reasonably believes they face an imminent threat of death or serious bodily harm. The insanity defense excuses criminal conduct when mental illness prevents the defendant from understanding the nature or wrongfulness of their act (M'Naghten) or from conforming their conduct to the law (MPC). Necessity (choice of evils) justifies criminal conduct when the defendant reasonably believes it was necessary to avoid a greater harm. Duress excuses conduct performed under a threat of imminent death or serious bodily harm.
Key Doctrines
- Self-defense (reasonable force, imminence, proportionality)
- Duty to retreat vs. stand-your-ground
- Castle doctrine
- Defense of others
- Insanity (M'Naghten test, MPC test, irresistible-impulse test)
- Necessity / choice of evils
- Duress
- Intoxication (voluntary vs. involuntary)
- Infancy
- Entrapment
Essential Cases
Exam Tips for Criminal Law
Always start by identifying the actus reus and mens rea for each offense. State the elements of the crime explicitly before applying the facts. If the question involves the MPC, use purpose/knowledge/recklessness/negligence; if common law, use specific intent/general intent/malice.
For homicide questions, systematically work through each degree of criminal homicide from most to least serious: first-degree murder, second-degree murder, voluntary manslaughter, involuntary manslaughter. Analyze each theory of murder (premeditation, depraved heart, felony murder) before moving to manslaughter.
On attempt questions, always address both the mens rea (specific intent to commit the target offense, even if the target offense is not itself a specific-intent crime) and the actus reus (substantial step under MPC vs. dangerous proximity at common law). Address impossibility if the facts raise it.
For self-defense, analyze every element: (1) honest and reasonable belief, (2) imminent threat, (3) unlawful force by the aggressor, (4) proportional response. Note whether deadly force is at issue and whether the jurisdiction follows duty-to-retreat or stand-your-ground rules.
Conspiracy is a separate, non-merging offense — a defendant can be convicted of both conspiracy and the completed crime. Always address Pinkerton liability for foreseeable crimes of co-conspirators.
When analyzing insanity, identify which test the jurisdiction uses (M'Naghten, MPC/ALI, irresistible impulse, Durham) and apply it to the specific facts. Remember that insanity is an excuse, not a justification, and the burden of proof varies by jurisdiction.
Felony murder requires identifying the underlying felony, confirming it is inherently dangerous (abstract or case-specific analysis), and checking for limitations: merger doctrine, res gestae (time and place), agency vs. proximate-cause theory for killings by third parties.
Do not confuse justification defenses (self-defense, necessity — the act was right) with excuse defenses (insanity, duress — the act was wrong but the defendant is not blameworthy). This distinction affects burden of proof, third-party liability, and scope.
Frequently Asked Questions
What is the difference between specific intent and general intent?
At common law, specific-intent crimes require the defendant to have a particular subjective purpose or objective beyond the actus reus (e.g., larceny requires intent to permanently deprive, attempt requires intent to commit the target offense). General-intent crimes require only that the defendant intentionally performed the prohibited act. The distinction matters for defenses: voluntary intoxication and certain mistakes of fact can negate specific intent but generally not general intent. The MPC replaces this framework with four defined mental states: purpose, knowledge, recklessness, and negligence.
What are the elements of felony murder?
Felony murder holds a defendant liable for murder when a death occurs during the commission of a dangerous felony, even without intent to kill. The elements are: (1) the defendant committed or attempted a qualifying felony (traditionally arson, robbery, burglary, rape, or kidnapping), (2) a death occurred during and in furtherance of the felony, and (3) there is a causal connection. Limitations include the merger doctrine (the underlying felony must be independent of the killing), the res gestae requirement (the killing must occur during the felony), and debates over liability when the lethal act is committed by a third party.
What is the MPC test for insanity?
Under the Model Penal Code (section 4.01), a defendant is not responsible for criminal conduct if, at the time of the conduct, as a result of mental disease or defect, they lacked substantial capacity either: (1) to appreciate the criminality (wrongfulness) of their conduct, or (2) to conform their conduct to the requirements of the law. This is broader than M'Naghten because it includes a volitional prong (inability to conform conduct) and uses 'appreciate' rather than 'know,' acknowledging that emotional understanding differs from intellectual awareness.
When can deadly force be used in self-defense?
Deadly force in self-defense is justified when the defendant reasonably believes they face an imminent threat of death or serious bodily harm, the threat is unlawful, and the force used is proportional. In duty-to-retreat jurisdictions, the defendant must retreat if they can do so safely before using deadly force (except in their own home — the castle doctrine). Stand-your-ground jurisdictions eliminate the duty to retreat. The initial aggressor generally cannot claim self-defense unless they effectively communicate withdrawal.
What is the difference between attempt and conspiracy?
Attempt requires the specific intent to commit a crime plus a substantial step toward completion (MPC) or coming dangerously close (common law). It is a unilateral act directed at a specific crime. Conspiracy requires an agreement between two or more people to commit a crime plus (usually) an overt act in furtherance. A key difference is that attempt merges into the completed offense (you cannot be convicted of both), while conspiracy does not merge (you can be convicted of both conspiracy and the completed crime).
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