Genesis 4:9

“And the Lord said unto Cain, where is Abel thy brother? etc.] Perhaps this was said to him the next time he came to offer, he not being with him: this question is put, not as being ignorant where he was, but in order to bring Cain to a conviction and confession of his sin, to touch his conscience with it, and fill it with remorse for it; and, for the aggravation of it, observes the relation of Abel to him, his brother: and he said, I know not; which was a downright lie; for he must know where he had left him or laid him: this shows him to be under the influence of Satan, who was a liar, and the father of lies, as well as a murderer from the beginning; and that he was so blinded by him, as to…”

“I know not--a falsehood. One sin leads to another.”

“- Section IV - The Family of Adam - Cain and Abel 1. קין qayı̂n, Qain (Cain), “spear-shaft,” and קנה qānah, “set up, establish, gain, buy,” contain the biliteral root קן qan, “set up, erect, gain.” The relations of root words are not confined to the narrow rules of our common etymology, but really extend to such instinctive usages as the unlettered speaker will invent or employ. A full examination of the Hebrew tongue leads to the conclusion that a biliteral root lies at the base of many of those triliterals that consist of two firm consonants and a third weaker one varying in itself and its position. Thus, יטב yāṭab and טיב ṭôb. So קין qayı̂n and קנה qānah grow from one root. 2. הבל…”

“And the Lord said unto Cain, Where is Abel thy brother? - God knew him to be guilty; yet he asks him, that he might draw from him a confession of his crime; for those who would be justified before God, must accuse themselves. And he said, I know not - Thus in Cain the devil was both a murderer, and a liar from the beginning. Am I my Brother's keeper? - Sure he is old enough to take care of himself, nor did I ever take charge of him. Art not thou his keeper? If he be missing, on thee be the blame, and not on me, who never undertook to keep him. Genesis 4:10”

“4:9 Where is your brother? The questions God asked Cain (4:6, 9, 10) recall those that God asked Cain’s parents (3:9-13). In both cases, humans put up evasive answers (cp. 3:12-13). Cain’s answer is shockingly defiant—another clue that the problem with his token offering was the attitude that lay behind it.”

“Where is: Gen 3:9-11; Psa 9:12 I know: Gen 37:32; Job 22:13, Job 22:14; Psa 10:13, Psa 10:14; Pro 28:13; Joh 8:44; Act 5:4-9 Genesis 4:10”

“Defiance grows with sin, and punishment keeps pace with guilt. Adam and Eve fear before God, and acknowledge their sin; Cain boldly denies it, and in reply to the question, "Where is Abel thy brother?" declares, "I know not, am I my brother's keeper?" God therefore charges him with his crime: "What hast thou done! voice of thy brother's blood crying to Me from the earth." The verb "crying" refers to the "blood," since this is the principal word, and the voice merely expresses the adverbial idea of "aloud," or "listen" (Ewald, 317d). (drops of blood) is sometimes used to denote natural hemorrhage (Lev 12:4-5; Lev 20:18); but is chiefly applied to blood shed unnaturally, i.e., to murder.…”