John Wesley on Genesis 4:9

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.