The witness of sacred history
The covenant between God and mankind is interwoven with reminders of God's gift of human life and man's murderous violence:
For your lifeblood I will surely require a reckoning.... Whoever sheds the blood of man, by man shall his blood be shed; for God made man in his own image.
The Old Testament always considered blood a sacred sign of life. This teaching remains necessary for all time.
Source: Catechism of the Catholic Church (Vatican.va)