By that logic, a judge might give a break to a conjoined criminal so there would be less harm to an innocent member of his immediate family (this being the most literal of "family ties"). But the two situations aren't exactly analogous: It sometimes happens that innocent people are harmed as a result of a family member being thrown in jail, but that's different from the state taking deliberate action to punish someone for a crime he didn't commit. To toss someone in prison along with his evil twin seems more like the latter. So even if, say, the sentence for a conjoined murderer were discounted by half, the good twin would still receive an unwarranted punishment.
There are some other possible solutions to the problem, however. You might throw both twins in prison but treat only the guilty one as if he were a convict. When the siblings were released, for example, the good twin would have all the rights of a normal citizen, while the evil twin would have lost the right to vote, be registered as a sex offender, etc. You might even compensate the good twin according to the relevant payout rules for wrongful convictions. (Those who were wrongly incarcerated for a federal crime can get up to $50,000 per year, or $100,000 if they were on death row.)
Of course, jail isn't the only way to punish a criminal. In a thoughtful analysis of the conjoined-criminal problem, law student Nicholas Kam considers several other kinds of sanction. Capital punishment seems out of the question, since the good twin might be killed as well. (You can't execute a pregnant woman in the United States, either.) So long as the legislature permitted it, the courts might impose a fine on the guilty twin instead of a prison sentence. But as Kam points out, it's been a long, long time since monetary sanctions have been used to punish violent crimes. It's also hard to imagine that a fine wouldn't affect the innocent twin as well.
Another possibility would be enforced separation. There's little chance that the courts would allow for this kind of violation of the body, however. Even if they did, the logistics would be prohibitive. The appropriate surgery can be extraordinarily complicated—one recent case took 26 hours and a small army of surgeons—and it doesn't always work. Still, there's at least one precedent for this situation: In 2000, a British court ordered the surgical separation of a pair of conjoined twins, known as Mary and Jodie, against their parents' wishes. Doctors had testified that both would die if the operation were not performed. (It was, and Jodie survived.)
All of the above assumes that one twin is unambiguously guilty, and the other is unambiguously innocent. In real life, it's hard to imagine such a clear-cut case. For example, a jury might be inclined to believe that the "good" twin acted as an accomplice, or perhaps an accessory, to the crime after the fact. This charge would apply if one sibling knew that the other had committed a crime—which seems likely under any circumstances—and that he intentionally provided assistance or comfort to his sibling rather than calling the police at the first opportunity. If the good twin were convicted of an accessory crime in federal court, he'd be subject to at most half the prison term appropriate to his evil brother. In some states, however, it's legal to harbor a fugitive if that person happens to be your sibling.
One more way that a "good" twin might be convicted, even if he took no part in the actual committing of the crime: In some states, he might be found guilty of not stopping his brother. Although as a general rule, common-law tradition dictates that you can't be held accountable for something you didn't do, 10 states have so-called "duty to rescue" statutes. These require innocent bystanders to call the police or reasonably attempt to aid a victim in distress. (In four of these states, siblings of the offender are exempt from the law.) If one twin tried to stab someone, the other might be expected to grab his arm or drag both of them to the ground. The penalty for failing to rescue is usually a fine, though some jurisdictions allow for up to a year in prison.
Bonus Explainer: Could an innocent conjoined twin be compelled to testify against her evil sibling? Absolutely. In the United States, spouses tend to have special privileges when it comes to testifying against each other. A handful of states offer similar protections to parents who don't wish to testify against their children. But siblings—conjoined or not—have no such right.
Got a question about today's news? Ask the Explainer.
Explainer thanks Richard Dieter of the Death Penalty Information Center, Nicholar Kam of the University of San Francisco, Dan Markel of the FSU College of Law, and attorney Michael Shollar.
Previous questions of the year:
2008: What is the most disloyal dog breed?
2007: Why don't we drop medical waste and nuclear waste into active volcanoes, the "ultimate high-temperature incinerators"?
2006: Can a bar of soap get dirty, or is it self-cleaning because it's soap?
Become a fan of the Explainer on Facebook.
TODAY IN SLATE
One of the most amazing feats in chess history just happened, and no one noticed.
The Extraordinary Amicus Brief That Attempts to Explain the Wu-Tang Clan to the Supreme Court Justices
Amazon Is Officially a Gadget Company. Here Are Its Six New Devices.
Do the Celebrities Whose Nude Photos Were Stolen Have a Case Against Apple?
The NFL Explains How It Sees “the Role of the Female”
Amazon Is Now a Gadget Company
How to Order Chinese Food
First, stop thinking of it as “Chinese food.”