Themes dealt with in Leviticus 35. Summed up nicely in verse 33: "Don't pollute the land in which you live. Murder pollutes the land. The land can't be cleaned up of the blood of murder except through the blood of the murderer."
Accidental murder got leniency. There were 6 cities set up that you could run to. Once inside you were safe.
Motivation was weighed. The tool involved in the murder was a significant part of the process.
16 "But if the killer has used an iron object, that's just plain murder; he's obviously a murderer and must be put to death.
17 "Or if he has a rock in his hand big enough to kill and the man dies, that's murder; he's a murderer and must be put to death.
18 "Or if he's carrying a wooden club heavy enough to kill and the man dies, that's murder; he's a murderer and must be put to death.
19 "In such cases the avenger has a right to kill the murderer when he meets him—he can kill him on the spot. "
So if you claimed to have killed someone accidentally, but the implement that killed the person was considered lethal - you were assumed to have had intent to kill, even if you claimed you did not.
There was always an avenger. Sort of like our present day police. I imagine the avenger was a man or group of men from the family of the deceased. It is assumed all throughout this passage that there is an avenger chasing the murderer. Justice is involved in allowing, or NOT allowing the avenger to take the life of the murderer as just compensation.
Motivation was a strong factor in every case. 20 -21 "And if out of sheer hatred a man pushes another or from ambush throws something at him and he dies, or angrily hits him with his fist and kills him, that's murder—he must be put to death. The avenger has a right to kill him when he gets him. "
The jury system was established. 22 -27 "If, however, he impulsively pushes someone and there is no history of hard feelings, or he impetuously picks up something and throws it, or he accidentally drops a stone tool—a maul or hammer, say—and it hits and kills someone he didn't even know was there, and there's no suspicion that there was bad blood between them, the community is to judge between the killer and the avenger following these guidelines. It's the task of the community to save the killer from the hand of the avenger—the community is to return him to his asylum-city to which he fled."
We have a double system of justice. The internal sense of fairness that says wrongs should be punished. And a legal system, based largely on the Bible, to weigh motives, involve the community, give mercy occasionally, and mete out punishment to the wrong doer.
A human legal system is never perfect.
But by and large, justice must be served for a people to live in peace.