Slager is charged with murder in the April 2015 shooting death
of Walter Scott
, an unarmed black man, after a traffic stop in North Charleston.
The case appeared headed for a mistrial, but the jury three times went back to deliberate Friday after indicating to the judge it was unable to gain a consensus.
During one deliberation, a male juror took the unusual step of writing the judge a note, saying he couldn't vote for a conviction and wouldn't change his mind.
"I still cannot without a reasonable doubt convict the defendant," the male juror wrote. "I cannot and will not change my mind."
A note from the foreman said that juror was the only one having the issue.
If convicted of murder, Slager faces 30 years to life in prison.
Judge Clifton Newman allowed the jury, which began deliberating Wednesday night, to consider the lesser offense of manslaughter, which carries a potential sentence of up to 30 years in prison.
South Carolina law says that a judge can only once instruct the jury to return to deliberate more. Newman did, and when the jurors returned, he explained they would have to consent to more time or they could indicate they were hopelessly deadlocked.
The foreman said they would continue to discuss the case.
After more time, the judge stopped them again and asked whether they were deadlocked still or needed further time. The jury could use more time, the foreman answered.
Jurors deliberated until about 6 p.m. Friday before Newman sent them home.
The jury of 11 white jurors and one African-American is considering the testimony of 55 witnesses given over the span of five weeks.
On the stand, Slager argued self-defense, saying he shot Scott as he ran away because Scott posed a threat and could have turned around and charged him.
One of the key pieces of evidence in the trial was a cell-phone video of the altercation
. In the video, Slager is seen chasing Scott, then shooting him in the back. Prosecutors said the two were 18 feet apart when Slager opened fire.
Slager, who is white, also is scheduled to go on trial early next year on federal charges, including civil rights offenses, related to the shooting.