Masei - Shishi
Some Killer Laws
G-d told Moshe about the cities of refuge, where someone who killed accidentally could flee. Those who killed by accident would be brought to such a city before their trials (see Talmud Makkos 9b). There were to be six such cities, three in Israel proper and three in Trans-Jordan.
Anyone who killed intentionally would be subject to execution by the courts. After conviction, he also might suffer vigilante justice at the hands of the victim's relative. The relative could take this justice wherever he finds the murderer. However, someone who killed without malice aforethought is not a murderer. (He might be criminally negligent, but he's not a murderer; it's for the courts to evaluate.) The court must mediate between the accidental killer and the relative seeking retribution. For his own protection, the clumsy killer goes to one of the refuge cities, where he is protected by law from vigilante justice. He must live there until the High Priest dies. (What's the relevance of the High Priest to this matter? As spiritual leader of the nation, the High Priest's merits play a role in whether or not such tragedies occur. See Rashi on verse 25.)
If the killer goes outside the city of refuge and the victim's avenger finds him - well, oops. He's outside his protected area and what happens, happens. If the avenger gets his retribution outside a city of refuge, he's not liable for murder.
After the High Priest dies, the killer is free to go home and the avenger can't touch him.
A murderer cannot be convicted on the testimony of a single witness; two are required.
You can't save a convicted murderer with money, nor can you buy an accidental killer's way out of a refuge city prematurely.
Finally, G-d cautions the people about bloodshed. It's a serious crime and it will defile the land, so they must not permit it to occur.