Just noticed this bit at Fr. Z's blog: "Ironically, as the Holy Father was being driven to the White House, the Supreme Court upheld 7-2 the legality of execution by lethal injection. Chief Justice Roberts wrote the opinion." Here's the story from Boomberg.
The case was not about the constitutionality of the death penalty per se, but about the means used to administer the penalty (lethal injection). The ruling says that lethal injunction does not violate the Eighth Amendment's ban on "cruel and unusual" punishment.