CHARLESTON, S.C. — They sat on the same courtroom bench, but worlds apart — the parents of Walter L. Scott, a black man shot to death in 2015, and Michael T. Slager, the white police officer who killed him as he fled after a traffic stop.

And the arguments they heard from lawyers were just as disparate as they pleaded with jurors to settle a bitterly divisive case in their favor: for the government, a rare conviction of a police officer, and for the defense, an acquittal of an officer seen on tape shooting a fleeing man.

“Our whole criminal justice system rides on the back of law enforcement,” Scarlett A. Wilson, the chief prosecutor for Charleston County, told the jury of 11 white people and a black man. “They have to be held accountable when they mess up. It is very, very rare, but it does happen.”

But Mr. Slager’s lawyer, Andrew J. Savage III, pressed jurors to resist “a false narrative” — that the officer malevolently opened fire toward Mr. Scott’s back on April 4, 2015, when he fled a traffic stop for a broken taillight — and to find that Mr. Slager had acted in self-defense.