Makkot 11 - Unintentional Killer and the High Priest
An unintentional killer who is exiled to a city of refuge can leave the city and go home upon the High Priest's death. This includes any High Priest: one who was anointed with oil or by wearing special garments, and even one who served temporarily. Rabbi Yehudah says, "Even the High Priest anointed for war." Therefore the mothers of High Priests would supply the exiles with food and clothing, so that they would not pray for their sons to die.
One whose sentence was finalized when there was no High Priest, one who accidentally kills a High Priest, or a High Priest who killed - these never leave the city of refuge.
One may not leave the city of refuge for testimony regarding a mitzvah, nor for testimony regarding a monetary dispute, nor for testimony regarding a capital punishment. Even if all Israel needs him, and he is like the general Yoav the son of Zeruyah, he does not ever leave.
If a killer left the boundary of the city of refuge and the redeemer of the blood found him, Rabbi Yose HaGligli says that it is a mitzvah for the redeemer to kill him, and everybody else is allowed to do so, but Rabbi Akiva says that it is permissible for the redeemer, and everybody else is liable to death for killing him.
Art: John Opie - The Murder of Rizzio