But Miller has an uphill battle. Most nations of the world, like Mexico, do not use capital punishment. Most of them will not agree to help the United States carry it out. When the offense for which extradition is requested is punishable by death under the laws of the requesting party and the laws of the requested party do not permit such punishment for that offense, extradition may be refused unless the requesting party furnishes such assurances as the requested party considers sufficient that the death penalty shall not be imposed, or, if imposed, shall not be executed. Instead, Mexico chose the lengthy extradition process.
Extradition is a fairly recent invention in human history.
Nations did not begin signing formal treaties until the 1700s. Before then, if you wanted to pluck somebody out of another country, you did it either by force, by trick, or by the consent of the other side's ruler. They require that the accused's acts be recognized as a crime in both places. They require that the accused be tried only for the specific crime alleged. They generally refuse to extradite for purely political crimes.