What do the "three nicks" represent in the novel, The Guardians?

The three nicks represent failures in the justice system. When Duke was convicted of raping and murdering Emily Boone, bite mark analysis was an accepted form of evidence. Since that time, the findings of many trials based on bite mark evidence have been overturned because that sort of evidence was so faulty. A supposed bite mark expert claimed that three nicks on Emily’s arm came from Duke’s teeth. Years later, this ruling was overturned when it was determined that the pubic hairs found on Emily’s body were not a DNA match to Duke.