If the person who caused the death was found not guilty of murder at a public trial before the community (compare Deuteronomy 19:11–12), that person had to remain in the city of refuge.
The avenger was not allowed to take revenge. The community had decided that the person was not guilty of murder.
until the death of the high priest: The death of the high priest likely served as a kind of expiation (a way of removing guilt or cleansing from sin) for the blood that had been shed. Even if the person did not commit murder, the spilling of human blood was believed to pollute the land (see Numbers 35:33; compare Genesis 4:10–11).