Charles Ellicott Commentary Numbers 35:31-32

"Moreover ye shall take no ransom for the life of a murderer, that is guilty of death; but he shall surely be put to death. And ye shall take no ransom for him that is fled to his city of refuge, that he may come again to dwell in the land, until the death of the priest." — Numbers 35:31-32 (ASV)

Moreover you shall take no satisfaction for the life of a murderer ... — The Israelites were not allowed to make terms with the relatives of the man who had been slain, as is not infrequently the case today; nor were they permitted to allow the man who had slain anyone unintentionally to return home from the city of refuge before the death of the high priest, on the payment of a sum of money by way of compensation.