Makkot 9 - Exile for Inadvertent Killing
A blind person who killed inadvertently is not exiled, since " without seeing " excludes him from responsibility - says Rabbi Yehudah. However, Rabbi Meir says that there is another exclusion, " without awareness ," and double negative becomes affirmative, so a blind inadvertent killer is exiled.
An "enemy" is one who deliberately avoided speaking to the victim of "accidental" killing for three days. An "enemy" is not exiled, because he can't claim accidental killing. Rabbi Yose says that an "enemy" is considered forewarned and is executed. Rabbi Shimon looks at the circumstances of the case.
There were three cities of refuge in Transjordan, and three in the land of Canaan. Direct roads were constructed to facilitate getting to a city of refuge. The court would provide the accidental killer with two Torah scholars, and they would try to dissuade the avenging relative from wishing to attack. Then the court would bring him from the city of refuge and determine the degree of his responsibility.
Art: Pieter the Elder Bruegel - The Parable of the Blind Leading the Blind 1568