Gen 4, 8-12 Cain attacked his brother Abel and killed him

(Gen 4, 8-12) Cain attacked his brother Abel and killed him

[8] Cain said to his brother Abel, "Let us go out in the field." When they were in the field, Cain attacked his brother Abel and killed him. [9] Then the LORD asked Cain, "Where is your brother Abel?" He answered, "I do not know. Am I my brother's keeper?" [10] The LORD then said: "What have you done! Listen: your brother's blood cries out to me from the soil! [11] Therefore you shall be banned from the soil that opened its mouth to receive your brother's blood from your hand. [12] If you till the soil, it shall no longer give you its produce. You shall become a restless wanderer on the earth."

(CCC 2259) In the account of Abel's murder by his brother Cain (Cf. Gen 4:8-12), Scripture reveals the presence of anger and envy in man, consequences of original sin, from the beginning of human history. Man has become the enemy of his fellow man. God declares the wickedness of this fratricide: "What have you done? The voice of your brother's blood is crying to me from the ground. And now you are cursed from the ground, which has opened its mouth to receive your brother's blood from your hand" (Gen 4:10-11). (CCC 1867) The catechetical tradition also recalls that there are "sins that cry to heaven": the blood of Abel (Cf. Gen 4:10), the sin of the Sodomites (Cf. Gen 18:20; 19:13), the cry of the people oppressed in Egypt (Cf. Ex 3:7-10), the cry of the foreigner, the widow, and the orphan (Cf. Ex 20:20-22), injustice to the wage earner (Cf. Deut 24:14-15; Jas 5:4). (CCC 2268) The fifth commandment forbids direct and intentional killing as gravely sinful. The murderer and those who cooperate voluntarily in murder commit a sin that cries out to heaven for vengeance (Cf. Gen 4:10). Infanticide (Cf. GS 51 § 3), fratricide, parricide, and the murder of a spouse are especially grave crimes by reason of the natural bonds which they break. Concern for eugenics or public health cannot justify any murder, even if commanded by public authority.