Ghosts of Mississippi (1996) on Netflix

Medgar Evers is a black civil rights activist in Mississipi, who was killed by a gunman. It is later suspected that Byron De La Beckwith, a racist, is the killer and he would be tried a couple of times and both trials ended in hung juries. For more than 30 years, Evers' widow Myrlie has been trying to bring De La Beckwith to justice and she believes that she has what it takes to bring him to trial again. However, most of the evidence in the old trial have disappeared but Bobby De Laughter, an assistant D.A., decides to do what he can to help her despite being warned that it might hurt his political aspirations and the strain it's causing on his marriage.