COLUMBIA, S.C. (AP) — The video was unambiguous: A white police officer fatally shot an unarmed black man in the back as the man ran away. [...] a South Carolina jury was unable to agree on a verdict in one of the nation's ghastliest police shootings, with a lone holdout forcing a mistrial. "There's a jury full of people and they cannot decide if it's illegal to shoot someone who is running away from you?" said activist Johnetta Elzie, who is black. Prosecutors plan to retry former officer Michael Slager, who is scheduled to be tried separately next year on federal charges that he violated Walter Scott's civil rights. At one point, a juror sent a letter directly to the judge saying he could not "with good conscience approve a guilty verdict" and that he was unlikely to change his mind. Randall Kennedy, a black Harvard University law professor and author of several books on race relations, had difficulty reconciling the law with the mistrial, which he called "frightening." Is it at all plausible that you have a man running and a police officer says, 'I'm firing in self-defense?'