“Capital Punishment: New Testament Teaching”, 1998, Fr. John A. Hardon, S.J., considered one of the most prominent Roman Catholic theologians of the 20th century. See bottom.
http://www.therealpresence.org/archives/Sacred_Scripture/Sacred_Scripture_014.htm

“There are certain moral norms that have always and everywhere been held by the successors of the Apostles in communion with the Bishop of Rome. Although never formally defined, they are irreversibly binding on the followers of Christ until the end of the world.” “Such moral truths are the grave sinfulness of contraception and direct abortion. Such, too, is the Catholic doctrine which defends the imposition of the death penalty.”

“Most of the Church’s teaching, especially in the moral order, is infallible doctrine because it belongs to what we call her ordinary universal magisterium.”

“Equally important is the Pope’s (Pius XII) insistence that capital punishment is morally defensible in every age and culture of Christianity.” ” . . . the Church’s teaching on ‘the coercive power of legitimate human authority’ is based on ‘the sources of revelation and traditional doctrine.’ It is wrong, therefore ‘to say that these sources only contain ideas which are conditioned by historical circumstances.’ On the contrary, they have ‘a general and abiding validity.’ (Acta Apostolicae Sedis, 1955, pp 81-2).”

about Fr. John A. Hardon, S.J.
http://www.mariancatechist.com/html/general/stjohnhardon.htm