As part of the stabilising of creation, God causes animals to fear humans and permits them to be taken as food. The right to all animal life belongs to God and we are only allowed to eat meat because he grants it. Having said that ‘everything that lives and moves can be used as food’, there has to be a further stabilising restraint that institutes safeguards against the killing of humans.
In Genesis 9:6, God institutes judicial killing of the murderer specifically because he or she has attacked the image of God. It is civil government (and not private individuals) which has been given the delegated authority of God to mete out capital punishment and the commandment is not rescinded under the New Covenant, as Romans 13 attests.