SUMMA THEOLOGICA THE DEATH PENALTY
God instituted the death penalty in Genesis 9:6 "Whoever sheds man's blood, by man shall his blood be shed." In the New Testament, in Romans 4.13, Paul says that the state, the figure of magistrates are ministers of God and that is not in vain that bear the sword for executing criminals. Jesus also reaffirmed the death penalty as punishment for crimes such as murder, saying to Peter, "All who take up the sword, die by the sword." (Matthew 26.52).
The death penalty is determined and executed by the state, can not be confused with revenge, God is the same, only in the Old Testament, the emphasis was on punishing the person who committed the crime, and the New Testament the emphasis is to combat the spiritual causes of crime. There is no contradiction in God and your love fits perfectly in your Justice.
By scribe Valdemar Mota de Menezes