Ibn Ezra: The Death of the High Priest (Masei)
Someone who accidentally kills another can flee to a city of refuge. The person seeking refuge is then restricted to that city until the high priest dies.
Tag: cities of refuge
Rashbam: Priest and Prison (Matot-Masei)
Numbers 35 describes the cities of refuge. Accidental killers find safety there, but also a prison – they must remain there until the high priest dies.