The jurors again saw the video, frame-by-frame at some moments, on Tuesday, as the man who recorded it, Feidin Santana, sat in the front row. Mr. Slager insisted that specific facts confirmed by the recording, including that Mr. Scott did not have the officer’s Taser when he was shot, were not apparent amid the stress and commotion of an encounter that occurred after Mr. Scott fled from a traffic stop for a broken taillight.

Instead, Mr. Slager said that he thought Mr. Scott was “running for some reason,” and that he felt he was outmatched and “going to lose” the struggle with Mr. Scott. Soon, according to Mr. Slager, Mr. Scott seized the Taser and appeared ready to fire it.

“I pulled my firearm, and I pulled the trigger,” said Mr. Slager, who said he suffered from nightmares after the shooting. “I fired until the threat was stopped, like I’m trained to do.”

By the time Mr. Slager squeezed the trigger of his Glock, Mr. Scott was at least 17 feet away, a distance Mr. Slager suggested he did not recognize in the chaos. Mr. Scott, whose family believes he initially fled because of unpaid child support obligations, crumpled to the ground.

Not long after the shooting, Mr. Slager dropped his Taser next to Mr. Scott’s body, a decision he could not easily explain on Tuesday, but one that prosecutors view as proof that he was trying to plant evidence to cover up a murder.

The murder statute in this state is a decidedly unembellished one: It defines murder as “the killing of any person with malice aforethought, either express or implied.” Although prosecutors have not brought conspicuous evidence of racial animus on Mr. Slager’s part, they have depicted him as an officer who broke the law and local policies, including one that stipulates that “the preservation of life must always take priority over apprehension of criminals.”

Until the Saturday morning when he killed Mr. Scott, Mr. Slager had not fired his handgun while on duty. But to prosecutors, and to a defense team plainly worried about Mr. Slager’s being seen as a rogue officer, his history of using other types of force could be crucial to the jury.