Cities of Refuge: Those Admitted to Obliged to Remain In, Until the High Priest's Death
Source: TTT
Numbers 35:25, 28
The assembly is to protect the manslayer from the hand of the avenger of blood. Then the assembly will return him to the city of refuge to which he fled, and he must live there until the death of the high priest, who was anointed with the holy oil. / because the manslayer must remain in his city of refuge until the death of the high priest. Only after the death of the high priest may he return to the land he owns.