So if he was so guilty (not even death penalty opponents can really muster up many tears over this convict), why was his execution so controversial? The answer lies in international law.
Medellin was born in Mexico and moved to the United States when he was three years old. After his original trial and conviction, he decided that he wanted to consult with the Mexican consulate, as it is the right of foreign nationals in another country to do under the 1963 Vienna convention. This right was, apparently, denied by the Texas judicial system, since there seemed to have been absolutely nothing the consulate could have done. Indeed, as it turned out, the Mexican government couldn't produce any arguments as to why Medellin shouldn't die on the merits — only procedural questions.
The Medellin case wound its tortuous way through the court system, twice going to the United States Supreme Court and the International Court of Justice in The Hague.
That set up the conflict: the International Court of Justice ordered the United States to spare Medellin's life, but Texas refused to do so. Eventually the Supreme Court found that the federal government (the Bush Administration) couldn't order Texas to spare the guy's life, since Congress hadn't actually implemented the 1963 Vienna treaty.
So Texas won out, and Medellin finally was executed for his crime, with lots of protests from the international types, but, strangely, not much argument from them about the rights of the victims Medellin killed.
