Moses
Deuteronomy 19:12ESV·traditional attribution

then the elders of his city shall send and take him from there, and hand him over to the avenger of blood, so that he may die.

Matthew Henry Presbyterian @wholebiblehenry

It was one of the precepts given to the sons of Noah that whoso sheddeth man's blood by man shall his blood be shed, that is, by the avenger of blood, Gen 9:6. Now here we have the law settled between blood and blood, between the blood of the murdered and the blood of the murderer, and effectual provision made, I.

Commenting on Deuteronomy 19:1-13

John Gill Reformed Baptist @doctorgill

Thine eye shall not pity him,.... This is not said to the avenger of blood, who is not to be supposed to have any pity or compassion on such a person, but to the elders, judges, and civil magistrates of the city to which he belonged, who took cognizance of his case; these were to show him no favour on account of his being a...

Geneva Bible Notes Reformed @genevanotes

Then the elders of his city shall send and fetch him thence, and deliver him into the hand of the avenger of blood, that he may die. (f) The magistrates.