"I wonder if this is part of his faith. Certain Catholics believe life is not to be taken by men of faith, even when serving in their role according to Romans.
Not saying it's the answer, but it's a ventured guess."
Certain Catholics include the Pope and the Curia. The Catechism of the Church opposes the death penalty in modern times as unncessary. Since there are alternatives, the Church opposes its use in this day and age.
Alito's response on the matter reflects a mature Catholic's view on the subject. Catholics are not REQUIRED to oppose the death penalty in the way that they are required to oppose abortion, but those who take their faith seriously, as Alito does, will be very careful before agreeing to mete out death. It is always wrong to slay the innocent. It is murder, whether an individual does it or the state does it, and those who commit the murder are liable to God for it.
So, Alito said that he was going to take the time to be very sure on each death case. Very sure of WHAT, one might ask? Sure of procedural matters? Probably not that. If he reasons like the serious Catholic that he appears to be, he is going to take the time to be very, very sure that the man to be executed is really, actually, beyond a shadow of doubt in his own mind, guilty of the underlying murder. If he is, then a serious Catholic like Alito might not stand in the way of the application of the death penalty, because there is no danger of an innocent person being executed in that case.
I expect that this will be a pattern for Alito in death cases. I expect he'll be "Go slow Alito" on death sentences. It perfectly fits the Catholic philosophy on this, and Alito's responses and history show me, anyway, that he thinks like a Catholic.