Rabbi David Milston, in his recently published book, “Eternity”, has an interesting observation regarding the cities of refuge.
Rabbi Milston notes that forty-two of the forty-eight cities of refuge were inhabited by Kohanim and Leviim. The killer is sent there because of an element of negligence that caused the death of another individual.
Perhaps if the killer would have been more careful and considerate, this tragedy would never have taken place.
Therefore, his rehabilitation comes by living among the most giving and considerate members of society, the Kohanim and Leviim.
Everyone is influenced by their environment. If one is surrounded by the educators of the Jewish people, who live a purely spiritual life, it will have a positive effect.
When the killer gets out upon the death of the Kohein Gadol, he will be a changed person.