Matthew Poole and continuators on Deuteronomy 19:12

12 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.

Either of the slain person, who were most likely to prosecute the murderer: or, of the murderer, because God would oblige even his own fellow citizens to prosecute him to death, that it might appear how hateful murder and the murderer is to God and ought to be to all men.

Demand him of the Elders of the city of refuge, who upon the hearing of the cause and the evidence of the murder were obliged to deliver the offender to justice.