Link to the article here.
The implication of Fastiggi's defense is that the Church's teaching on capital punishment is neither of the deposit of faith nor is it an obvious precept (or permission) of the Natural Law. In which case, then no mere affirmation or denial of the liceity of capital punishment as being of the Gospel (or of Sacred Tradition) now suffices, as it must be given a justification through moral theology and evaluated accordingly.
I have no real difficulty with the claim that the teaching on the liceity of capital punishment is not a revealed datum. But that it is not of the Natural Law, I need to see an actual argument for that.