The New International Version of the Bible explains Genesis 4:9 is the verse where Cain asks God, "Am I my brother's keeper?" The moment illustrates God's knowledge that Cain killed his brother, Abel. This story is the first instance of murder in the Bible.
Cain and Abel are the sons of Adam and Eve, the first humans on Earth, according to the Bible's story on the origin of humankind. Cain becomes jealous of Abel after God favors Abel's plant crops over Cain's fatty portions of meat from his flock of sheep. Cain takes Abel out to their family's field and murders him. God punishes Cain by banishing him to the land of Nod, east of the garden of Eden.