Numbers 35

After God gave Moses instructions on how to divide the land for the tribes receiving an inheritance, God gave him instructions for cities for the Levites. They would be responsible, in part, for the justice system in the cities of refuge and teaching people God's statutes.

Blood defiled the land in a unique way, and the system of cities of refuge and setting up trials for people who had killed someone was set up, along with who exacted the penalty for murder, and how someone might be convicted.