How would the American legal system punish conjoined twins if one committed a murder while the other was completely innocent?


Let’s consider, for the sake of argument, that we are dealing with dicephalic parapagus conjoined twins, conjoined twins with two heads sharing one body. Each twin controls one half of the body, neither can control the other’s half of the body, and neither can feel what the other feels. This is the physiology of the Hensel twins, Abigail and Brittany Hensel. Further, you must accept that these are two separate individuals because: 1) they have two separate consciousnesses, 2) they exhibit distinct personalities, or 3) they each had to pass the driving exam. They are entangled singletons – two consciousnesses in one continuum of skin whose individuality is defined partly by their conjoining (see bio-ethicist Alice Domurat Dreger).

When considering the punishment for one guilty conjoined twin, it is necessary to put aside all of the factual considerations that may arise when one conjoined twin commits a murder to the detriment of her innocent, connected sibling. Put aside the idea that the innocent twin had any control over the guilty twin’s hand. Put aside the idea that the court may impute the guilty action to the innocent twin, finding her an accomplice in the commission of this murder. Put aside the idea that the court could find that the innocent twin had some duty to stop the murder from occurring. To accept any of these ideas is to find the conjoined twins entirely innocent or entirely guilty and runs outside the scope of this problem. Accept, for the purposes of this problem, that the jury has found one twin guilty and the other is merely an innocent bystander — she did not participate in the act nor could they have stopped the homicide from occurring.

The question posed is not purely speculative. According to 18th century French historian Henri Sauval, a murder of the kind presented was perpetrated in the 17th century by Italian conjoined twins. Born in 1617 in Genoa, two boys were held together by the stomach. One twin was completely healthy while the other was mute, deaf, and blind. Sauval records that the healthy twin stabbed a man to death and was tried, convicted, and sentenced to death. However, the twin was not executed “on account of the innocence of one of its component halves.” It was impossible to put one to death without twin killing the other. Unfortunately, Sauval failed to mention whether they were subsequently incarcerated or released after the death sentence was commuted, leaving this scenario ripe for legal analysis in the abstract.

Findings of Guilt

Before dolling out punishment, there must be a finding of guilt. The Fifth Amendment of the Constitution provides “No person…shall be deprived of life, liberty, or property, without due process of law.” When we speak of due process, we speak of fundamental fairness: the prosecution must prove all of the elements of a crime beyond a reasonable doubt through a fair procedure before a fair finder of fact. Crimes deal with conduct which society deems anti-social and therefore deserving of punishment. The term conduct is used in a broad sense to cover the two distinct components of a crime: 1) the act and 2) the state of mind accompanying the act. Therefore, when the Legislature passes a law outlawing a particular crime it will include a definition of the act and the requisite mental state to commit the crime. A crime cannot be consummated without fulfilling both of the elements of act and intent.

Under federal law, murder is defined as follows: “Murder is the unlawful killing of a human being with malice aforethought.” 18 U.S.C. § 1111(a). Here, Congress has defined the act of murder as “the unlawful killing of a human being” while the state of mind to commit a murder is “malice aforethought.” Malice aforethought is one of those lofty legal concepts that exists mainly so scholars can debate its meaning. Essentially, malice aforethought is a deliberate intention to take away the life of a “fellow creature,” according to the California Penal Code. Cal. Penal Code § 188.

In order to convict someone of murder, the prosecution must prove beyond a reasonable doubt that the accused committed the proscribed act and harbored this requisite mental state. The paradox presented with this problem is that although we have two inextricable entwined people, only one twin can be convicted of the crime. As in most criminal prosecutions, the jury serves as the finder of fact and must make the determination of guilt. For the purposes of this argument, we must suppose that only one twin can be convicted of the crime. Otherwise there is no legal dilemma. Once there has been a finding of guilt, the court attempt to determine the punishment for this crime, being ever respectful of the innocence of one of the twins.


The broad purposes of the criminal law are to make people do what society regards as desirable and to prevent them from doing what society considers to be undesirable. To achieve this end, the State allocates punishment for bad acts as opposed to rewards for good acts, emphasizing the discouragement of undesirable rather than the encouragement of the desirable. There are several theories underlying punishment, each with specific ends and particular means. These theories include:

Deterrence — Deterring the criminal or society (by way of example) from committing crime by giving him an unpleasant experience such as jail time.

Incapacitation — Incapacitating the criminal by removing him from society to protect the populous from further criminal conduct.

Rehabilitation — Rehabilitating the criminal through appropriate treatment or training.

Retribution — Retribution, or justice, is imposed on criminals by society for the wrongs they have caused.

Proposed Punishments

1. Capital Punishment

The death penalty stands as the most impractical of all the potential punishment choices. As there is only one conclusively guilty actor in the pair, the court would have to find a way to kill only the guilty twin. In the novel The Siamese Twin Mystery by Ellery Queen (1933) the authors considered the practical angles of this problem, including how to electrocute one Siamese without damaging the other, and in the end resolved the problem by clearing the twins of the crime. Depending on the extent of the conjoining, which in this case is substantial, it is likely impossible to kill one without killing the other. While this punishment would protect society from further harm by either twin, the execution of an innocent person runs so afoul of due process and the morals of American society, capital punishment cannot be used in this case.

2. Life Without Parole

As an alternative to the death penalty, Courts hand down sentences of life without parole. This represents sufficient leniency by the court but still raises constitutional concerns of jailing an innocent person for the duration of her life. Again there is the problem of denying someone their liberty without convicting them of a crime. There lies an exception to this doctrine under the criminal law for criminal forfeitures. This is when the State seizes property used in the commission of a crime (houses, cars, boats) even though the true owner had no knowledge of its illicit use. Under this doctrine, the injured, innocent owner can seek remittance of the property from the State. This concept lends itself by analogy to a murder involving only one conjoined twins. The State would presumably be in its rights to seize the unlawfully used property (i.e. their shared body) but the innocent twin would be given the opportunity to remit forfeiture in their body as a “joint tenant in common.”

3. Separation

To consider more extreme approaches to punishing the guilty twin, the Court could order the twins separated so that the guilty twin may be punished. Even if this Solomonic option were possible in this case, as physiologically it appears impossible, this action raises grave Constitutional concerns. The Supreme Court has held that the body to be inviolate, providing slim exceptions to this rule as in the testing blood alcohol content, chemical castration, and the death penalty. This punishment smacks of the Sharia law practice of chopping off a convicted thief’s hand. Furthermore, it is hard to argue that separation would only punish one of the twins as each would be left immobile, one half of a complete body. Separation surgeries have some success as in the case of Jodie and Mary Attard (although this surgery was undertaken knowing full well that it would and did kill the weaker twin). Modern scholars estimate the rate of successful separation surgery at around 5% (see also the Bijani twins). With such dismal rates, sentencing conjoined twins to separation surgery would be the equivalent of a death sentence.

4. Suspended Sentence

If the Court finds that the Constitutional limits of due process are so great that neither twin may be punished, the Court may be obligated to let the twins go free. This would be the ultimate downward departure from sentencing guidelines. Exercising this option calls to attention the balancing of American morals: which do we hold higher, the punishment of an innocent life or freeing a guilty one? To allow a convicted murderer to go free spits in the face of retribution and that holy notion of justice. Furthermore, Justice Scalia might argue, this option yields the ultimate killing machine: a person who cannot be punished for murder because their physiology precludes punishment. In light of this concern remember that the circumstances of the murder are so unlikely that it has only occurred once in known history. However, say the conjoined twin did kill again, it is hard to imagine that a jury could bifurcate the finding of guilt across the twins for a second time.

5. Monetary Sanctions

Finally, monetary sanctions may satisfy the underlying problem presented. While it is hard to accept monetary sanctions in the place of traditional punishment, this option may be the only permissible alternative. Primitive and ancient societies relied on a form of tort damages, known as “wergild,” to compensate the families of murder victims and to control crime. The Germanic tribes had some success with this option until the Norman Conquest of the 9th century which did away with the practice. The problem with this punishment is that the average person would be reticent to assign a monetary value to surrender his life as he would get no utility from the money. Tort law, on the other hand, provides monetary compensation in wrongful death lawsuits, assigning millions for the loss of life. However, here we speak of the criminal law of murder, not the civil law of tortious liability. Monetary sanctions have never been popular in the modern era. Additionally, it is hard to argue that monetary sanctions would affect only one member of a conjoined twin pair.


As actors under American criminal law, conjoined twins present paradoxical obstacles to the application of traditional methods of criminal punishments. The Western notion of individuality precludes such duplicitous beings from orthodox measures to remedy criminal action, particularly the crime of murder. Constitutional limitations of due process and guarantees of life, liberty and property militate against equal treatment of these actors under the law. I believe that within our Constitutional framework, the only thing to be done in this situation is to release the conjoined twins. Even if the jury sentenced the conjoined twins to death, the court would have to commute the sentence and release the twins. The guarantees of due process under the Fifth and Fourteenth Amendments prohibit punishing an innocent actor. Furthermore stare decisis, the doctrine that states that courts must follow the precedent of preceding and higher courts, presents an additional danger. If the court decided to punish the innocent twin despite her innocence, there would be nothing to stop the State from punishing others who have not been convicted of committing crimes (see also enemy combatants, plea of not guilty by reason of insanity, etc.).

While this solution may seem like a grave injustice to society, consider the innocent parties injured through mistrial, the criminals released because of shortcomings of shoddy police work, and statutes of limitations preventing the delayed filing of charges despite ironclad certainty. Such is the nature of our legal system. With these limitations come the freedoms and guarantees of the Constitution, preventing an overreaching government from undue interference into the lives of private citizens and frivolous legal action.



Chained for Life (1951). A dramatization of the situation presented.

Those Extraordinary Twins by Mark Twain (ebook provide by Project Guttenberg).

Tom Waits Interviews Tom Waits. In this interview Tom Waits offers the story of a conjoined twin who committed a murder in 1890 in Baltimore. As far as I can tell, there is no merit to this story.

Hard cases make bad law.