Makkos, chapter two, mishnah 3. This mishnah deals both with the nature of the victims of accidental killing and with the nature of those who do the killing: which of those who kill accidentally goes into exile, and for whose killing does one go into exile.
Who goes into exile and for killing whom:
A father goes into exile for accidentally killing his son, and a son goes into exile for killing his father.
Anyone goes into exile for killing a Jew. The Gemara notes that this applies even to a Canaanite slave and a Kusi who accidentally killed a Jew; they too are obligated to go into exile.
A Jew goes into exile for killing them, including a Canaanite slave or a Kusi whom he killed accidentally.
An exception: if he killed a ger toshav, a resident alien, the Jew does not go into exile.
That is one way to read this line of the mishnah. But there is another version, and this is the version followed by most of the commentators and by the Mishnah itself, and in fact it is the Gemara's version as well: it is not this way but the reverse. According to that version, a ger toshav does not go into exile for killing a Jew, and the reason is that a Noahide does not require a warning - there is no need for anyone to warn him, for the very fact that the Torah warned him not to do this is itself the warning. But a Jew who killed a ger toshav does go into exile.
The mishnah continues and establishes that a ger toshav goes into exile only when he killed another ger toshav.
A blind man who killed:
Rabbi Yehudah holds that a blind man who killed a person does not go into exile, for the verse says "belo re'os" - without seeing, which implies that only in this instance did he not see, but ordinarily he was able to see; whereas a blind man is not able to see at all. The Rambam adds another reason: a blind man is close to being under compulsion. He is closer to doing an act not accidentally but against his will, as one compelled, rather than as one who acts accidentally - where there is inattention but also a certain level of responsibility.
Rabbi Meir disagrees and says: "goleh" - the blind man does go into exile. He derives this from the fact that in addition to the limiting phrase "belo re'os," there is also the limiting phrase "bivli da'as" - without knowledge. And since we have two limitations here, a limitation after a limitation, it comes to do the opposite - to include; and in this case, according to Rabbi Meir, it comes to include the blind man.
An enemy who killed:
The mishnah continues: an enemy does not go into exile. One who hates another person, and it is known that he hates him, does not go into exile, because we assume that he is close to being intentional - too close to the intent involved here, and there is a level of negligence in it, so he is not a complete accidental killer. And the definition of an enemy is: anyone who has not spoken with his fellow, out of hatred, for three days.
Rabbi Yose bar Yehudah says: "hasoneh neherag" - the enemy is put to death, even without a warning, even without anyone having warned him, "vaharei hu k'mu'ad" - and he is treated as one already forewarned. This is because Rabbi Yose bar Yehudah holds that no warning is necessary, since its entire purpose is to distinguish between an accidental and an intentional killer, and here there is a presumption that he did it with premeditation.
Rabbi Shimon says: "yeshno goleh v'yeshno she'eino goleh" - there is a case where he goes into exile and a case where he does not. It depends on the circumstances. There are instances in which the enemy goes into exile, and there are instances in which he does not. "V'zeh haklal" - and this is the rule, says Rabbi Shimon:
"Kol sheyachol lomar ladaas harag - ein goleh": if it is possible to say that he killed intentionally, he is not exiled. He is certainly considered close to an intentional murderer, and although we cannot put him to death according to Rabbi Shimon, we also cannot send him into exile, since he is not a true unintentional killer.
"Veshelo ladaas harag - harei zeh goleh": if it appears that even though he was an enemy, the circumstances testify that the act was genuinely unintentional, he is exiled, despite being an enemy.
In summary: in this Mishnah we learned which unintentional killers are exiled and for killing whom - a father and a son, a Jew, a Canaanite slave and a Kusi, and the law of a ger toshav according to the two versions; the dispute between Rabbi Yehudah and Rabbi Meir concerning a blind man who killed, based on the limiting phrases "belo re'os" and "bivli da'as"; and the law of an enemy, who is not exiled because he is close to an intentional murderer - according to Rabbi Yosi bar Yehudah he is even put to death without a warning, and according to Rabbi Shimon it depends on the circumstances of the act.