Charleston, South Carolina (CNN) A prosecutor vowed Monday to retry a white former police officer charged with killing an unarmed black motorist in North Charleston, South Carolina, after the jury failed to reach a verdict following 22 hours of deliberation.

The judge declared a mistrial on the fourth day of deliberations in the murder trial of Michael Slager, the former North Charleston officer.

"We will try Michael Slager again," 9th Judicial Circuit Solicitor Scarlett A. Wilson said in a statement expressing disappointment that Slager was not convicted in the five-week murder case in state court.

Slager shot and killed Walter Scott , 50, after an April 4, 2015, traffic stop. The shooting was captured on a bystander's cell phone video, which showed Scott running away as Slager fired eight times, striking Scott three times in the back.

The jurors -- 11 whites and one African-American -- struggled to reach a consensus. They returned to deliberate three times Friday after indicating they were deadlocked. One juror, in a note, said he couldn't vote for a conviction and wouldn't change his mind. Monday brought a slew of questions, such as requests for clarifications on terminology related to the law, before the mistrial was declared.

Family 'not sad'

"Every human being, no matter what color you are, can see (what happened on the video), unless you already made up your mind," Scott family attorney L. Chris Stewart said.

Stewart told CNN that, despite reports of jurors' questions and requests, his team's research indicates the breakdown was 11 jurors to one, and the lone holdout ignored the evidence and testimony in the case. Still, he said, he's emboldened because, before the trial, observers expressed doubt the proceedings would be fair, given the jury makeup. But "all the other white jurors were with us," Stewart said.

"We are not worried," he said of a retrial. "That was just Round 1. He's getting retried immediately, and the (U.S. Department of Justice) is coming after him."

The ruling disappointed Scott's family, attorneys and supporters. They said they were relying on their religious faith and believe Slager ultimately will be convicted.

"Injustice will not prevail," Judy Scott, Walter Scott's mother, said after the mistrial was declared. "He will get his just reward."

Slager is scheduled to go on trial early next year on federal charges, including civil rights offenses, related to the shooting. Wilson, in her statement, said she hoped the federal and state courts will coordinate efforts regarding future trial dates.

Judy Scott said Monday she was "not sad."

"And I want you to know why I'm not sad, because Jesus is on the inside," she said. "And I know that justice will be served because the God that I serve, he's able. He told me to wait on the Lord and be of good courage, and God, he is strengthening my heart."

Earlier, jurors passed a note to the judge that said, "Despite the best efforts of our members we are unable to come to a unanimous decision."

Jurors are thanked by each side

Wilson thanked jurors for their service, saying even though she is disappointed she respects their decision.

JUST WATCHED Watch the video that's key to the Michael Slager case Replay More Videos ... MUST WATCH Watch the video that's key to the Michael Slager case 01:30

Wilson urged jurors not to let "anyone from the outside get in your head" and make them question their decision.

"Y'all seen every minute of this trial," she said. "You have sacrificed more than any of your peers."

Wilson said she hoped to speak with the jurors to gain insight into the strength of their case.

Defense attorney Andy Savage also thanked the jury for its service. "The rule of law has to be preserved in this country," he said.

There are no degrees to the murder charge in South Carolina, and if convicted, Slager faced 30 years to life in prison. The state had to demonstrate "malice aforethought" in Slager's actions, even if it was just for a second.

Judge Clifton Newman had also allowed the jury to consider the lesser offense of voluntary manslaughter, meaning the killing happened in the heat of passion. That charge carries a potential sentence of up to 30 years in prison.

The jury's questions Monday included requests for clarification on terminology such as "heat of passion," "malice aforethought" and whether there were different laws for police officers. Heat of passion means committing an act in the moment, without prior intent. Malice aforethought means having the intent to cause death or harm.

On the stand, Slager had argued self-defense, telling jurors he shot Scott as he ran away because he posed a threat and could have turned around and charged him.

A key piece of evidence in the trial was the cell phone video, which showed Slager chasing Scott, then shooting him in the back. Prosecutors estimated the two were 18 feet apart when Slager opened fire.

Savage had argued the media created a "false narrative " of a white officer in North Charleston who stopped a black motorist for a brake light and just shot him when he ran away. The brief cell phone video didn't tell the whole story of the encounter, Savage said.

"There's a lot of bravado being spoken by the local prosecutor and a lot of politics in this case," Savage told CNN.

Justice 'delayed'

Stewart, the Scott family lawyer, said: "He dodged it by a hair and he's not dodging it again."

He reiterated the sentiment of the Scott family that Slager will be convicted. Stewart said: "Our faith is unwavering. ... We aren't worried. We don't need to scream or shout because we know that it's coming. It's just been delayed."

Walter Scott's brother Anthony called for peaceful protests in Charleston, and said: "We feel like our voices need to be heard."

"And we need to let the nation know that we're not happy, but we're not sad because we know that God got it," Anthony Scott said.

After the trial, some in the area's African-American community expressed disappointment in the outcome. The murder case coincided with the trial of white supremacist Dylann Roof, who is charged with killing nine church members at the historically black Emanuel African Methodist Baptist Church on June 17, 2015.

Is there forgiveness in your heart?

"We never see a win," pastor and community activist Thomas Dixon told CNN affiliate WCIV-TV. "Our people need to get something in the win column when it comes to these officer-involved shootings. I don't believe justice was served today."

The shooting of Scott was one of several killings of unarmed black men by law enforcement caught on video, including the shooting of Philando Castile in Minnesota and the chokehold death of Eric Garner in New York. The deaths have led to protests nationwide about allegations of police misconduct in cases involving black men.

In a statement, Wilson said prosecutors were grateful to Walter Scott's family for their "patience, understanding and cooperation with us."

"The Scotts have been a sterling example of dignity and grace in extraordinary circumstances," Wilson said.

Charleston Mayor John Tecklenburg said he was "deeply disappointed" in the outcome.

"However, despite that disappointment, I also understand that justice is not always delivered by a single jury, in a single courtroom, on a single day," the mayor said in a statement. "Justice is often a journey. And the journey to justice in the Michael Slager case is far from over."

In a press conference, Anthony Scott was asked if he could forgive Slager, like the family of the victims of Emanuel AME forgave Roof, who is accused of opening fire in a Bible study.

"In my heart, I will find the peace to forgive Michael Slager for doing that ... but at this present time, until my family can see justice, no, there's no forgiveness," he said.