On a March morning in 2017, Tamera Moore, a 38-year-old woman living in the southeast Oklahoma town of Valliant, began the day with a bitter argument.

She and her boyfriend, Geoffrey Briley, began quarreling and she told him she wanted to break up. He grabbed her neck, threw her onto a bed and began biting her face and lips, court records say. He left, and Moore went to the hospital.

For months, police, prosecutors and even a judge pleaded with her to testify in court. But Moore refused, and prosecutors dropped the charge in June.

Two months later, Moore was found dead – shot in her home. Poli...