From the "timeless catechism" of St. Robert Bellarmine (published in 1598):
Princes and Magistrates are provided with public authority and so kill evildoers, but not as the masters of their lives, but as ministers of God, as St. Paul witnesses. God willed and commanded for evildoers to be punished, and--if they were to merity the penalty--be killed so that the good could abide securely and peacefully. For that reason God gave Princes and Magistrates a sword in their hand to exercise justice, defend the good but punish the wicked. Thus when a criminal is killed at the command of a public authority of this sort, it is not said to be murder, but an act of justice. Therefore, one ought to avoid understanding the authority of the commonwealth in the Commandment "thou shalt not kill."
Did doctrine change? (No, it cannot)
Was Bellarmine wrong? (After the Church said he was right; at least until recently)
Remember, this has been referred to as a "timeless catechism" for centuries now. If those who reject the universal position of the Church on capital punishment (regardless of who they are, or how high in the Church hierarchy they happen to be!) want to say that what was "timeless" is now "timebound" (i.e. no longer true) they are going to have do a lot more than get sentimental. They are going to have to prove that the basic Catholic principle that theology does not change, has suddenly become wrong.