Taking the stand for the first time during his five-week murder trial, Slager said that even at 18 feet away, Scott still posed a threat and could have turned around and charged him.
"Scott would never stop after I gave him multiple commands to stop," said Slager in response to questioning by Deputy Solicitor Bruce DuRant, one of the state's prosecutors.
Slager had testified that he and Scott scuffled before the shooting and that Scott was much stronger. Slager said he couldn't remember all the details but recalled Scott wrestling away his Taser and briefly pointing it at him.
"I knew I was in trouble," he said.
"I was in total fear that Mr. Scott didn't stop, continued to come towards me."
That's when Slager said he pulled the trigger.
Where was the Taser?
During cross-examination, the prosecutor played the widely seen cell phone video of Scott's shooting in court frame-by-frame while asking Slager for his account of the incident.
After the tussle, the cell phone video showed Scott running away with the Taser rolling on the ground behind Slager.
"So would you agree that at this time he is not armed and he's running away from you?" DuRant asked.
"Like I said at the time on April 4th, I would say no, but after watching the video, yes," Slager replied.
DuRant questioned how the Taser could've posed a threat to Slager 18 feet away.
"Would you agree that even if Mr. Scott had that Taser, it could not have been used against you at the distance depicted on that video?" he asked.
"At that time, I didn't have that information, so I can't answer that question," Slager replied.
He said he didn't know where the Taser was at the time.
Other highlights from Slager's testimony:
-- The former officer said his life since the shooting has been a "nightmare" and expressed regret over the episode. "My family has been destroyed by this. The Scott family has been destroyed by this," he said.
-- Slager broke down in tears when he recalled missing the birth of his son in May 2015 because he was in jail.
-- DuRant asked Slager to confirm that he had "18 use of force incidents in four years." Slager confirmed this after checking his notes.
-- While in jail, Slager said the prisoner in his adjacent cell was Dylann Roof, who is accused of killing nine people
at a black church in Charleston in June 2015. Roof is currently on trial in a courthouse across the street.
Slager's defense team, led by attorney Andy Savage, rested its case Tuesday. As the trial winds down, new details have emerged from the defense and prosecution about the day the officer killed Scott.
Those details have painted different narratives of what happened.
Slager stopped Scott for a taillight violation on April 4, 2015. When Slager returned to his patrol car to run Scott's license, Scott bolted from his car. A foot chase ensued. Eventually, a witness' cell phone video captured Slager shooting the unarmed man in the back.
Here's how each side has argued the case in court:
What the prosecution says
Scott's decision was foolish, but he didn't deserve death.
In her opening statement for the prosecution, Solicitor Scarlett Wilson said Scott decided to run because he knew that once Slager ran his license, he would go to "debtors' jail." That's because a warrant had been issued for Scott over unpaid child support.
Wilson described Scott's decision to run as foolish. But while he deserved to be prosecuted, he did not deserve to die, she said.
"We're here to bring accountability to Michael Slager for his choices, for his decision to go too far. For his decision to let his sense of authority get the better of him. For his decision to shoot an unarmed man in the back five times. To try to shoot him eight times," Wilson said.
Investigators: Video counters officer's claims.
Agents from the South Carolina Law Enforcement Division testified that they were concerned by discrepancies between what they saw in the video and what Slager said happened the day of the shooting.
A video presented to the jury did show a struggle, and the men were tangled on the ground with Taser wires.
The defense has argued that Scott was able to take the Taser away from Slager and was coming at the officer with the Taser.
But Agent Angela Petersen said the video did not show the "Taser being taken away, the shell casings in relation to where the body was, and the fact that Mr. Scott (was) running away."
When DuRant asked Petersen if the video matched what she had been told happened at the scene, she said it did not.
Scott was far away from the officer when he was shot.
Cell phone video showing Scott running away from Slager when he was shot prompted widespread criticism from the public. The autopsy performed on Scott's body showed entry wounds on his back and side.
The prosecution has argued that the distance between Slager and Scott proved that the officer's actions were premeditated. They were not in "close contact," as the officer has said.
Wilson, the solicitor, showed that distance for the jury in court using a measuring tape. She said it was 17 feet when the first bullet was fired from Slager's firearm and more than twice that distance when the last bullet was fired.
Witness: Slager was always on top during the struggle.
Feidin Santana said he saw Slager in a foot chase with Scott. Santana followed the two men into a lot where he saw part of the incident before he began filming. Only the tail end of the altercation was caught on camera.
Santana described a struggle in which the officer was always on top, and Scott was trying to get away. He said they got up quickly.
What followed, Santana said, was "something I'll never forget, he (shot) the man running."
What the defense says
Slager was an exceptional, hard-working officer.
Defense attorney Andy Savage said Slager was an officer with an exceptional record. He said Slager worked for $43,000 a year in the most crime-ridden, under-patrolled area in North Charleston while supporting a pregnant wife and his two young stepchildren.
Scott had refused to comply.
The defense played audio from Slager's conversations with dispatch to the jury. In the audio, Slager gives Scott multiple warnings to "stop" and multiple warnings that he was going to fire his Taser.
Savage argued it was Scott's failure to comply with the officer's demands that led to the escalation in use of force.
Slager feared for his life.
During an interview with South Carolina Law Enforcement Division agents in April 2015, Slager said he feared for his life because Scott was calling out his location to someone on his phone during the encounter.
Slager said he was worried about not seeing his family again because he did not know who else might be coming.
The person on the other side of the phone turned out to be Scott's mother, who testified in court that she heard her son say, "They Tasing me."
If Slager is to be found guilty of murder, the state must demonstrate "malice and aforethought" in the officer's actions -- even if it was for just a second before the shooting.
There are no degrees to the murder charge in South Carolina. If convicted, Slager faces 30 years to life in prison.
The defense team will continue to call experts and witnesses this week.
Slager also faces a potential trial early next year on federal charges related to the shooting, including civil rights offenses.