Yeah, I'm sick of people claiming Cruz is only standing up due to encouragement from Trump or that no one has ever stood up for the victims of illegal immigrant crime before. In the case you speak of (Medellín v. Texas) Ted Cruz did those things and far more.
In that case Cruz faced down the Bush administration and Mexico who wanted the death penalty dropped. What Cruz won was a win for Texas state sovereignty, National Sovereignty, and justice for the victims of José Ernesto Medellín.
Medellín v. Texas, 552 U.S. 491 (2008), is a United States Supreme Court decision that held that even if an international treaty may constitute an international commitment, it is not binding domestic law unless Congress has enacted statutes implementing it or unless the treaty itself is "self-executing." Also, the Court held that decisions of the International Court of Justice are not binding domestic law and that, without authority from the United States Congress or the Constitution, the President of the United States lacks the power to enforce international treaties or decisions of the International Court of Justice.
Medellín v. Texas
And for those unaware of what kind of animal the US and international establishment wanted spared from the death penalty.
On June 24, 1993, José Ernesto Medellín (an 18-year-old Mexican citizen) and several other gang members participated in the murder of Jennifer Ertman and Elizabeth Peña, when they raped a 14-year-old and 16-year-old girl for an hour in Houston, Texas. Both girls were killed to prevent them from identifying their assailants. Medellín strangled one of the girls with her own shoelaces. Hours after Medellin's arrest he admitted to his part in the crime and boasted of having "virgin blood" on his underpants.
To his credit, Rick Perry rejected calls for further delays of Medellín's execution and he was executed at 9:57pm on August 5, 2008.