Sforno on Genesis 9:5/ספורנו על בראשית ט׳:ה׳

1ואך את דמכם לנפשותיכם אדרוש, although I will not punish you for spilling animal’s blood, I will hold you responsible for shedding the blood of fellow human beings. Human beings, all human beings, are more precious to Me than the lives of animals. This retribution for spilling the blood of human beings may on different occasions be applied in different ways: It all depends on the worthiness of the person under attack or potential attack. If, for instance, the person deserves saving, the words מיד כל חיה אדרשנו ומיד אדם are meant in the preventive sense, i.e. G’d will save such a person’s life be it under attack from animals or from human beings. If, in the eyes of G’d, the person under attack does not deserve being saved from violent death, this still did not give the animals or other human beings the right to kill him. Therefore, in such instances, ipso facto, G’d will exact retribution from the killers.

2This is the meaning of the apparently redundant words מיד איש אחיו אדרוש את נפש האדם, where the word אדרוש refers to the life of a human being that has already been killed. We find the word אדרוש in both senses depending on circumstances, compare Ezekiel 34,10. The emphasis on איש את אחיו, refers to G’d exacting such retribution from humans for killing humans, seeing that this is not their nature, or should not be their nature. He will not exact retribution from an animal which killed a human being who, in G’d’s eyes, had already forfeited its right to live.