New Defender's Study Bible Notes
4:9 I know not. Cain thus added blatant lying to his sins of self-righteous pride and murder. However, in one sense, he was speaking the truth. He knew where Abel’s blood was spilled but not where Abel himself was. Abel was now the first human inhabitant of Sheol (or Hades), that place in the heart of the earth where departed spirits would reside while awaiting the coming of the Savior (Luke 16:22-26; Ephesians 4:8-10; I Peter 3:18-20).