3 so that anyone who kills a person accidentally and unintentionally may flee there and find protection from the avenger of blood.

Read Joshua 20:3 Using Other Translations

That the slayer that killeth any person unawares and unwittingly may flee thither: and they shall be your refuge from the avenger of blood.
that the manslayer who strikes any person without intent or unknowingly may flee there. They shall be for you a refuge from the avenger of blood.
Anyone who kills another person accidentally and unintentionally can run to one of these cities; they will be places of refuge from relatives seeking revenge for the person who was killed.