NORTH CHARLESTON, S.C. -- The white South Carolina police officer charged with murder for shooting an unarmed black man in the back was allowed to stay on the force despite a 2013 complaint that he used excessive force against another unarmed black man.

In an exclusive interview with The Associated Press, Mario Givens recounted Wednesday how he was awakened before dawn one morning by loud banging on the front door of his family's North Charleston home.

On the porch was Patrolman Michael Thomas Slager, the officer now charged in the shooting death of Walter Lamer Scott, which was captured in dramatic cellphone footage by a bystander Saturday.

Givens, who was clad only in a T-shirt and boxer shorts, cracked open his door and asked what the officer wanted.

"He said he wanted to come in but didn't say why," said Givens, now 33. "He never said who he was looking for."

Then, without warning, Slager pushed in the door, he said.

"Come outside or I'll tase you," he quoted the officer as saying, adding: "I didn't want that to happen to me, so I raised my arms over my head, and when I did, he tased me in my stomach anyway."

Givens said the pain from the stun gun was so intense that he dropped to the floor and began calling for his mother, who also was in the home. At that point, he said another police officer came into the house and they dragged him outside and threw him to the ground. He was handcuffed and put in a squad car.

Though initially accused of resisting the officers, Givens was later released without charge.

Asked about the 2013 incident on Wednesday, North Charleston police spokesman Spencer Pryor said the department plans to review the case to see whether its decision to exonerate Slager was correct. Pryor said he had no timetable for the review.

Givens' relatives remember the encounter vividly.

"It was very devastating," said Bessie Givens, 57, who was awaked by her son's piercing screams. "You watch your son like that, he's so vulnerable. You don't know what's going to happen. I was so scared."

It turned out that Givens' arrest was a case of mistaken identity. Officers had been looking for his brother, Matthew Givens, whose ex-girlfriend had reported that he came into her bedroom uninvited, then left when she screamed and called 911.

The woman, Maleah Kiara Brown, told The AP on Wednesday that she and a friend had gone to the Givens home with the officers and were sitting outside when Slager knocked on the door. The second officer had gone around to the back of the house.

She had provided the officers with a detailed description of her ex-boyfriend, Matthew Givens, who is about 5 feet, 5 inches tall. Mario Givens stands well over 6 feet.

"He looked nothing like the description I gave the officers," Brown said. "He asked the officer why he was at the house. He did it nicely. The police officer said he wanted him to step outside. Then he asked, 'Why, why do you want me to step outside?' Then the officer barged inside and grabbed him."

Moments later, she saw the police officers drag Mario Givens out of the house and throw him in the dirt. Brown said she kept yelling to the officers that they had the wrong man, but they wouldn't listen. Though Givens was offering no resistance, she said, she saw Slager use the stun gun on him again.

"He was screaming, in pain," she said. "He said, 'You tased me. You tased me. Why?' It was awful. Terrible. I asked the officer why he tased him and he told me to get back."

"He was cocky," she said of Slager. "It looked like he wanted to hurt him. There was no need to tase him. No reason. He was no threat -- and we told him he had the wrong man."

She said she later told a female police supervisor what she had seen.

The next day, an angry Mario Givens went downtown to police headquarters and filed a formal complaint. He and his mother say several neighbours who witnessed what happened on the family's front lawn also contacted the police, though they say officers refused to take their statements.

The incident report filed by Slager and the other officer, Maurice Huggins, provides a very different version of events. In the report, obtained by The AP through a public-records request, Slager wrote that he could not see one of Givens' hands and feared he might be holding a weapon. He wrote that he observed sweat on Givens' shirt, which he perceived as evidence that he could have run from Brown's home, and then ordered him to exit several times.

When Givens didn't comply, Slager said he entered the home to prevent him from fleeing and was then forced to use his stun gun when Givens struggled with him. The officers' report describes the Givens brothers as looking "just alike."

After Mario Givens filed his complaint, the department opened an internal investigation. A brief report in Slager's personnel file says a senior officer was assigned to investigate. After a couple of weeks, the case was closed with a notation that Slager was "exonerated."

Brown is listed as a witness in the investigative report, but her purported statement included none of the details she said she provided about Slager shocking Givens while he was on the ground. She said she was never contacted as part of the police investigation and had not spoken with anyone about that night until she was contacted by an AP reporter Wednesday.

The report includes statements from Givens and from another woman who was there that night, Yolonda Whitaker, who said she saw Slager stun Givens "for no reason." Efforts to reach Whitaker by phone and the addresses listed for her in the police report were unsuccessful.

Givens said he was never contacted as part of the internal investigation and learned the case had been closed only after he went to the station about six weeks later and asked what happened.

"They never told me how they reached the conclusion. Never. They never contacted anyone from that night. No one from the neighbourhood," Givens said.

Givens shook his head Wednesday when asked about his reaction to learning Slager had been charged with murder. Slager is being held without bail.

"It could have been prevented," Givens said of Scott's death. "If they had just listened to me and investigated what happened that night, this man might be alive today."