Dual Criminality and How Offenses Are Matched

Dual criminality is the requirement that the conduct for which a person is sought be a crime in both the requesting and the requested state. It sounds like a formality and it is frequently the whole of the contest, because legal systems that developed independently divide human conduct into offenses in different ways, and the request arrives described in a vocabulary the receiving court does not use.

What the requirement asks

The statutory hook is short. A judicial officer may certify a case only where the evidence is sufficient to sustain the charge under the provisions of the proper treaty. The treaty defines which offenses are extraditable, and in the modern form it does so by requiring that the conduct be punishable in both states. The judge therefore performs a translation: taking the acts described in the foreign request and asking whether those acts, if committed in the United States, would violate American criminal law.

Two things follow. The requesting state's own characterization does not control, because a label carries the structure of a legal system rather than a description of behavior. And the absence of an identically named American offense proves nothing, since the same conduct may be prosecuted here under a differently organized statute.

Conduct rather than labels

Courts have consistently rejected an element-for-element comparison. The inquiry is whether the acts alleged are criminal in both jurisdictions, allowing for differences in how the offenses are defined, graded and named. A foreign offense of aggravated deception may correspond to wire fraud; a foreign offense of abuse of trust may correspond to embezzlement; a foreign homicide grading scheme may not align with any American one and still describe conduct plainly criminal here.

What defeats the requirement is a substantive gap rather than a definitional one. Conduct that is simply not an offense in the requested state cannot satisfy dual criminality however the request is framed. That gap arises with offenses defined by status or association, with speech and expression offenses, with certain regulatory and currency offenses, and with conduct criminalized abroad that American law affirmatively protects.

A recurring complication is which American law supplies the comparison. Federal courts have variously looked to federal criminal law, to the law of the state in which the person was found, and to the law of a preponderance of the states, and the treaty itself sometimes specifies. The choice can be decisive for conduct that is criminal in some states and lawful in others, and it should be settled by reading the treaty before the case law.

Where the matching breaks down

Fiscal and revenue offenses have a long history of exclusion. Older treaties commonly declined to reach tax and customs matters altogether, on the view that one state should not enforce another's revenue laws. Newer instruments generally include them, sometimes with a clause stating that extradition may not be refused merely because the requested state's tax system differs. Which regime applies is a treaty question, and the answer changes the outcome entirely.

Inchoate liability produces a second recurring dispute. Conspiracy as an American offense has no close analogue in some civil law systems, which reach the same ground through participation and association doctrines with different requirements. A request framed as conspiracy therefore invites an argument about whether the conduct alleged, rather than the theory of liability, is criminal in both places.

Extraterritorial conduct produces a third. Where the acts occurred outside the requesting state and are charged on an effects or nationality theory, the comparison asks whether the requested state would assert jurisdiction over comparable conduct. Many treaties address this expressly, providing that extradition shall be granted for an offense committed outside the requesting state where the requested state's law would allow prosecution in corresponding circumstances.

Older treaties avoid all three problems by not asking the question. A list treaty makes extraditability a matter of looking up the offense in a schedule annexed to the instrument, and an offense absent from the list is not extraditable no matter how serious it is or how clearly it would be criminal in both states. The certainty is real, and so is the cost: the schedule reflects the criminal law of the era in which it was negotiated, and offenses that did not exist then are simply outside it until the treaty is renegotiated or supplemented.

How it is litigated

The argument is made at the extradition hearing and, if certification follows, in a habeas petition. The materials are the treaty, the foreign charging documents authenticated under the diplomatic certificate provision, and the domestic statutes proposed as analogues. Because the rules of criminal procedure do not apply, there is no discovery mechanism to compel a fuller description of the conduct, and the analysis proceeds on what the request supplies.

Two practical points shape the work. The comparison should be made against the conduct described in the supporting affidavits rather than against the offense heading, since a heading that sounds foreign frequently conceals a familiar set of facts, and a heading that sounds familiar sometimes conceals conduct that is not criminal here at all. And the analysis should be conducted offense by offense, because a request commonly contains several charges and dual criminality can fail on some while succeeding on others, which matters directly under the rule of specialty.

The requirement is one element of the broader inquiry described in international extradition, it is assessed at the same hearing that tests identity and sufficiency, and it can arise even earlier where a person has been taken into custody under provisional arrest before the formal papers exist. Nothing comparable applies between states, where the asylum state asks only whether a crime is charged under the demanding state's law among the four reviewable issues.