Targum Pseudo-Jonathan on Genesis 9:5 extends the reach of divine justice to places human courts cannot follow. The blood of your lives I will require of every animal which hath killed a man, I will require that it be put to death on his account. And from the hand of the human being, from the hand of the man who hath shed the blood of his brother, will I require the life of man.
Look at the sequence. First, even an animal that kills a human is held accountable. This is the Torah's astonishing teaching that human life is sacred enough that even a creature without reason is answerable for its spilling. The Sanhedrin centuries later would formalize this into laws about the goring ox.
Second, and more searchingly: from the hand of the man who hath shed the blood of his brother. The Targum uses the word brother. Every murder in Torah's imagination is a repetition of Cain and Abel. Every victim is a brother. The first crime after Eden was fratricide, and every murder since rhymes with it.
The takeaway the Maggid leaves on this verse: Jewish justice looks at a corpse and sees a sibling. Where human courts fail, heaven does not. Life is guarded by a witness who never sleeps.