Say what you will about the death penalty, to me this is just another case of people not knowing all the facts before jumping to the conclusion that the action must be correct or it wouldn't have been taken.
This execution was in violation of the Vienna Convention, a treaty this country signed several decades ago. By choosing to ingore a treaty the United States agreed to abide by, the Texas state government has placed at risk United States citizens detained all over the world. It has also undermined the US's ability to call for anyone else to abide by promises made by their governments. And for what? Vengence? Ghandi had it right: "An eye for an eye soon leaves everyone blind."
Also not mentioned in the "description of the crime" is the fact that Mr. Medillan was barely 18 years old at the time of the offenses. Even if there were absolutely no errors made in his trial, there is no escaping the fact that but for a matter of months, he would not have been eligible for execution. Unless you've actually read something about this case, you really have no idea what the facts of this case entail...