Module 1: Actus Reus, Mens Rea & Concurrence

Almost every crime is built from the same handful of pieces: an actus reus (a voluntary act, or a legally-required omission), a mens rea (the required guilty mental state), often specific attendant circumstances and a result the act must cause, and — tying it together — concurrence between the act and the mental state. Miss any required piece, and the crime as charged generally isn’t made out, however bad the underlying facts look.

Morissette v. United States shows how seriously courts take the mens rea piece, even when a statute doesn’t mention it. A man collected spent bomb casings from an Air Force practice range, genuinely believing they were abandoned junk, and sold them for scrap — the federal conversion statute he was charged under said nothing at all about intent. The Supreme Court refused to read it as a strict liability crime anyway: mens rea is such a deeply rooted feature of criminal law that courts presume Congress meant to require it, even from statutory silence, unless Congress clearly says otherwise. Skipping a required piece isn’t just disfavored — courts will read a missing piece back into the statute rather than accept its absence.

Example. Peter throws a rock through John’s window on purpose. The act (throwing the rock) is the actus reus; his intent to break the window is the mens rea; the broken window is the result his act caused; and because he intended the breaking at the exact moment he threw the rock, concurrence is satisfied too. All the pieces line up — that’s what makes this a complete crime, not just an unfortunate accident.

Actus reus requires a voluntary bodily movement — one the defendant actually willed. Reflexes, convulsions, movements during a seizure, sleepwalking, or hypnosis all fail this test, no matter how harmful the result. Relatedly, the law can’t punish someone for a mere status — under Robinson v. California, criminalizing a condition itself (rather than an act or omission) is unconstitutional.

People v. Decina shows how courts handle voluntariness when the seizure itself isn’t the whole story. A man with a known history of epileptic seizures drove anyway, had a seizure behind the wheel, and struck and killed several people. He argued the seizure that actually caused the crash was involuntary, just like the candle-knocking example below — but the court looked one step earlier in the chain: the truly voluntary act was his decision to get behind the wheel at all, knowing his condition made a seizure a real possibility. Actus reus doesn’t always have to be the literal, final movement that caused the harm — an earlier voluntary choice that knowingly created the risk can supply it instead.

Example. Peter, mid-seizure with no warning or prior diagnosis, involuntarily knocks a lit candle onto a curtain, starting a fire. However serious the fire, Peter’s knocking the candle over wasn’t a voluntary act — it can’t itself supply the actus reus of an arson charge. Compare that to a city ordinance that simply makes it a crime to “be an addict” with no act required at all — that’s an unconstitutional status crime under Robinson, since it punishes a condition, not conduct.

The general rule is stark: there is no duty to rescue a stranger at common law, however easy and safe the rescue would be. An omission only becomes criminal if a legal duty to act existed, from one of five recognized sources: a statute, a special relationship (parent-child, spouses), a contract, voluntary assumption of care (once begun, it generally can’t be abandoned in a way that leaves the victim worse off), or creation of the peril (even innocently).

Jones v. United States is the real case courts still cite for this exact list of duty sources. A woman was convicted of manslaughter for letting an infant in her care starve to death, but the trial never actually asked the jury to find that she had a legal duty toward the child in the first place — the appeals court reversed, laying out these same categories (statute, status/relationship, contract, and voluntary assumption of care) as the only recognized sources of a duty to act. Without the jury deciding which, if any, applied on these facts, the conviction couldn’t stand — a moral failure, however severe, still isn’t a crime without a legally recognized duty underneath it.

Example. Peter, an excellent swimmer with zero relationship to John, watches John struggle in a public lake and does nothing — no crime, however troubling that seems, since a stranger owes no general duty to rescue. Now compare three variations: if Peter is John’s parent (special relationship), if Peter is a paid lifeguard on duty (contract), or if Peter accidentally knocked John into the water in the first place (creation of the peril) — in every one of those versions, Peter now has an affirmative duty to act, and his inaction can support criminal liability.

At common law, crimes are often sorted into general intent (requiring only intent to perform the act itself) and specific intent (requiring an additional, particular purpose beyond the act). The distinction matters most for defenses like mistake of fact and voluntary intoxication, which apply more readily to specific intent crimes.

People v. Hood shows exactly why courts bothered drawing this line: voluntary intoxication defenses. A man who was extremely intoxicated shot and wounded a police officer, then argued his drunkenness meant he never formed the intent required for assault with intent to commit murder. The California Supreme Court held voluntary intoxication can negate the specific intent an aggravated assault charge requires, but cannot negate the general intent needed for simple assault — the same drunken shooting could defeat one charge while leaving the other fully intact, purely because of which category the crime fell into.

Example. Battery is typically general intent — Peter intentionally swinging and striking John is enough, with no further purpose required. Burglary, by contrast, is specific intent: breaking and entering a structure is only burglary if Peter also intended, at the moment of entry, to commit a felony once inside. Peter breaking into a shed just to sleep, with no further criminal purpose, is trespass — not burglary — because that extra specific intent is missing.

The MPC replaces the sometimes-muddy general/specific intent labels with four defined mental states, roughly a hierarchy from most to least culpable: purposely (conscious objective to cause the result), knowingly (practically certain the result will occur, without necessarily wanting it), recklessly (actually, subjectively aware of a risk and consciously disregarding it), and negligently (a reasonable person would have perceived the risk, even though this defendant genuinely did not). The negligently/recklessly line is the one most often tested: recklessness requires actual awareness; negligence does not.

Example. Peter wires a mailbox to explode because he wants it destroyed — that’s purpose. If he mainly wants to scare the owner but is practically certain the blast will also destroy a nearby fence he doesn’t care about, that’s knowledge as to the fence. If Peter instead fires a gun into the air at a party, aware there’s a real risk of hitting someone but disregarding it because he doubts it’ll happen, that’s recklessness. And if Peter leaves a loaded gun on a table around small children, never even considering the obvious risk a reasonable adult would have caught, that’s negligence.

The Model Penal Code was drafted by the American Law Institute in 1962 as a model statute for states to adopt or adapt — it isn’t binding federal law anywhere on its own. Roughly two-thirds of U.S. states have adopted all or major parts of it since, which is exactly why modern criminal law courses (and modern statutes) increasingly speak in terms of purposely/ knowingly/recklessly/negligently rather than the older common-law general/specific intent labels — but a real minority of states, and federal criminal law itself, still lean heavily on the older common-law framework, so both vocabularies genuinely matter.

Elonis v. United States (2015) shows the purposely/knowingly line still getting litigated at the Supreme Court, generations after the MPC coined it. A man convicted of making threatening interstate communications (posting violent, threatening-sounding material about his ex-wife on Facebook) argued he never subjectively meant the posts as real threats — the lower courts had instead asked only whether a reasonable person would view them as threatening, an objective, negligence-style standard. The Court reversed: a true threats conviction requires the defendant’s own subjective mental state, at least recklessness, not merely what a reasonable listener would think — reinforcing that “knowingly” and “recklessly” genuinely mean something different from “a reasonable person should have known,” even in a modern statute that never uses the MPC’s own labels.

A narrow but real exception: some crimes require no mens rea at all. Good faith, reasonable care, or an honest mistake is simply no defense. This shows up mainly in minor regulatory or public-welfare offenses (health, safety, and environmental rules with modest penalties) and, in many jurisdictions, in statutory rape as to the victim’s age.

Staples v. United States shows how reluctant courts are to expand this exception beyond its narrow, traditional lane. A man was charged under a federal statute requiring registration of machine guns, for possessing a rifle that had been secretly, invisibly modified to fire automatically without his knowledge. The government argued the statute was strict liability — possession alone was enough, regardless of whether he knew the gun’s true firing capability. The Supreme Court disagreed: absent a clear statement from Congress, courts won’t presume strict liability for a felony carrying serious prison time and involving an item (an ordinary-looking rifle) that isn’t inherently and obviously dangerous the way the classic regulatory strict-liability offenses are.

Example. Peter’s factory exceeds a pollution-discharge limit despite his genuinely careful, good-faith effort to comply. If the regulation is strict liability, his care and good faith don’t matter — the violation itself is enough. This is exactly why strict liability is controversial: it breaks the usual link between blameworthiness and punishment that mens rea normally protects, which is also why courts and legislatures keep it narrow rather than the default rule.

The mental state and the act have to exist at the same time. It’s not enough that a defendant once wanted a particular outcome if the act that actually caused it happened later, disconnected from that earlier intent. Concurrence doesn’t care how old an intent is — only whether it’s genuinely present at the moment of the act.

Thabo Meli v. The Queen is the classic case testing concurrence’s outer limit — a “single transaction” the defendants believed had already finished. The defendants beat a man, believed him dead, and then rolled his body off a cliff to stage an accident — but he was actually still alive after the beating and died only later, from exposure after the fall. Their defense argued no single moment matched murderous intent to the actual cause of death: the intent existed during the beating, but the fatal act was the (they thought, harmless) disposal. The Privy Council rejected that, treating the beating and the disposal as one continuous transaction rather than artificially slicing it into separate acts — concurrence doesn’t always require pinpointing the exact instant of death to the exact instant of intent, where the whole sequence was really one ongoing plan.

Example. At noon, Peter angrily wishes John’s fence would fall down, then forgets about it entirely. At 3pm, with no memory of that wish, Peter’s car accidentally rolls into the fence, knocking it down exactly as he’d wished. No concurrence — the 3pm act was a genuine accident, unconnected to the faded noon wish, so there’s no intentional crime here despite the outcome matching. Now compare: if Peter, still consciously angry, deliberately steers into the fence at 3pm on purpose, concurrence is satisfied — the three-hour-old plan is still present and operating at the exact moment of the act, which is all concurrence actually requires.