Another system worth looking at is the Biblical "cities of refuge". Israel at the time was structured much like the Norse culture you're describing: each family or clan was self-governing. It was expected that the family of a murder victim would seek revenge. However, murder had a precise definition (malice was required, though specific intent to kill wasn't) and conviction required the testimony of two witnesses under oath. This is obviously hard to enforce when the "sentence" is being decided and carried out by the enraged relatives of the victim.
Unlike all the other clans, which had received actual territories, the priestly families (the Levites) just received cities scattered throughout the holdings of the other clans. Some of these were designated as "cities of refuge", and someone falsely accused of murder could flee to one of these cities for protection. The avenger could then come to the city and present charges to the priests, who would conduct a trial. Since the Levites were an entirely separate lineage from everyone else, they were fairly impartial in clan disputes.
If the accused was found guilty, he'd be handed over for execution; otherwise, he would stay in the city of refuge, in protective custody, until the death of the current high priest. This gave the victim's family time to cool off so they wouldn't do anything stupid.
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