Charleston, SC (WLTX) - A former South Carolina police officer will spend 20 years in prison for shooting and killing an unarmed man in North Charleston, a case that drew international attention and sparked a debate about the use of force by law enforcement.

U.S. District Court Judge David Norton handed down the sentence Thursday against Michael Slager for the death of Walter Scott. The decision followed a four-day hearing where prosecutors and defense attorneys made their final push for either harsh punishment or leniency for the former patrolman.

"I wish I could go back in time to change the event, but I can't," Slager said to the court before he was sentenced. "It's a very tragic situation and I'm sorry for it."

Norton used as his guideline for sentencing a penalty that would be appropriate for someone who was guilty of second-degree murder, saying Slager's crime was done with malice and forethought. He also said Slager obstructed justice by lying to South Carolina Law Enforcement Division agents after the incident.

Norton had a range of between 19 and 24 years in prison that he could have given Slager.

"No matter what sentence I give, neither the Scott family or the Slager family is going to like it or think it is right," Norton told the court.

The ex-officer has the right to appeal the sentence.

Before he was sentenced, Scott's mother, Judy Scott, spoke to the court, and offered compassion to her son's killer.

"I forgive you Michael Slager," she said. "Forgiveness is in my heart there and I pray for you that you would repent and let Jesus come into your life. You can come to Jesus, just as you are and he will forgive you."

Scott's brother, Anthony Scott, said it was tougher for him. "Forgiveness came easy for them," he said of his other relatives. "It came very hard for me."

He said when he and Walter were children, they used to play "cowboys and indians," and they learned from Western shows that you "never shoot a man in the back or shoot an unarmed man."

Slager's family had a chance to talk too, and his mother said her son didn't shoot Scott in anger or prejudice.

"I know this will be on his heart for the rest of his life," Karen Sharp said. "I want you to know that he is a very good person and we all love him very, very much."

Walter Scott

Slager shot and killed the 50-year-old Scott following a traffic stop for a busted taillight on April 4, 2015 while Slager was a member of the North Charleston Police Department. The incident was initially reported as case of an officer defending himself. But a cell phone video shot by Feidin Santana surfaced days later that showed the final seconds of the encounter. In it, Scott could be seen running away from the officer, and Slager was shown pulling out his gun and firing five shots into Scott's back.

Slager was promptly fired from his job and charged with murder.

The former cop and his attorneys had long argued that the cell phone video didn't show the full story, and that the officers truly feared for his life.

Michael Slager testifies on November 29, 2016.

During final statements Wednesday sentencing, Jared Fishman, one of the prosecutors in the case, admitted that Scott did not obey commands during the stop--including running from the officer after he was pulled over--but that doesn't justify what happened.

"The killing of Walter Scott was not justified," Fishman said. "It is time to call the killing what it really was. It was a murder."

Slager's lawyer, Andy Savage, didn't argue that his client committed a crime, but felt that it was voluntary manslaughter, not murder. He said that Slager and Scott had physically struggled before the shooting, and that explained the officer's state of mind.

The case was ultimately heard in federal court after U.S. attorneys reached a plead deal with Slager earlier this year. In exchange for the plea, the local prosecutor agreed to drop the murder charge against him..

At the time, Slager admitted to using excessive force, and he told the open court that his force was "objectively unreasonable."

Slager's first trial on the murder charge, held a year ago, ended in a mistrial, when jurors were unable to reach a unanimous verdict. The panel spent nearly 20 hours over four days deliberating before the judge agreed that they were hopelessly deadlocked.