What justice system does the Ibo culture have before the white men arrive in Things Fall Apart?

The core ideal of traditional Igbo justice is founded not so much on retribution but on restitution. Igbo justice attempts to create balance and to right wrongs instead of just punishing the perpetrator. The idea is to ensure that justice also ensures recompense for the victim as much as meting out punishment to the criminal.

There is a distinction between divine laws and laws made by humans. The breaking of divine law results in severe punishment (these would for example be crimes such as murder and incest - these are taboo). Transgressing man-made laws (such as theft) would result in less severe punishment.

Punishment for serious offences could result in execution, banishment or permanent compulsory exile. In this instance, restitution to the victim's family could be in the form of awarding the perpetrator's land and property to them or 'a life for a life'. 

Punishment for lesser crimes involved the criminal either being ostracized or having to pay compensation to the victim. The criminal might also be publicly humiliated and held up for derision by the villagers.

Traditional courts comprised the elders of the village (the egwugwu, comprising men only) who would then consult with the gods to establish punishment once a guilty verdict had been reached. The 'audi alteram partem' rule is applied. Both parties were given the opportunity to present their version of a matter. There was no formal court building or complex, and trials were conducted openly. Both parties had to undertake an oath in which they promised before their gods that they would tell the truth.

Based on the evidence presented, the egwugwu would then, after consultation with the gods, decide on the degree of illegality (the severity of the crime) and would decide on compensation or mete out punishment.

Okonkwo for example, was instructed to pay a fine after dishonouring The Week of Peace by beating his wife, Ojiugo, for not preparing him a meal. He was later banished to his mother's village, Mbanta, for seven years for accidentally shooting and killing one of Ezeudu's son during Ezeudu's funeral.