Other defendants who have been acquitted in other countries and then convicted on appeal have attempted to raise the double jeopardy principle to avoid extradition, without much success, said Mary Fan, a law professor at the University of Washington who specializes in cross-border criminal law.
The text of the treaty prevents extradition if the person has already been convicted or acquitted of the same offense by the "requested" country, which would be the United States in Knox's case because Italy would be requesting extradition from the United States. Because Knox was never prosecuted or acquitted for homicide in the United States, the treaty's double-jeopardy provision would not prevent Knox's extradition, said Fan.
While the issue is rare in the United States, several courts have rejected the double jeopardy argument in similar cases. In 2010, a federal court in California found that a man who was acquitted of murder in Mexico and later convicted after prosecutors appealed the acquittal, could not claim double jeopardy to avoid extradition to Mexico. That court cited a 1974 decision from the 2nd U.S. Circuit Court of Appeals in New York, that reached the same conclusion with respect to Canadian law, which also allows the government to appeal an acquittal.