NORTH CHARLESTON, S.C. » Dashboard video shows a police officer making a routine traffic stop. Cellphone video shows the officer shooting the fleeing motorist in the back. What remains a mystery is what happened during the minutes in between that led the police officer to become a killer.

The dash cam footage released by state police on Thursday showed North Charleston Officer Michael Thomas Slager pulling over black motorist Walter Scott for a broken brake light last weekend. Slager, who is white, has been charged with murder in Scott’s death.

Saturday’s traffic stop opens like so many others as Scott was stopped in a used Mercedes-Benz he had purchased days earlier, footage from the patrol car showed. At the outset, it’s a strikingly benign encounter: The officer is seen walking toward the driver’s window, requesting Scott’s license and registration. Slager then returns to his cruiser. On the dash cam video, Slager never touches his gun during the stop. He also makes no unreasonable demands or threats.

The video also shows Scott beginning to get out of the car, his right hand raised above his head. He then quickly gets back into the car and closes the door. After Slager goes back to his patrol car, minutes later, Scott jumps from his car and runs. Slager chases him.

What’s missing is what happens from the time the two men run out of the frame of dashboard video to the time picked up in a bystander’s cellphone video a few hundred yards away. The cellphone footage starts with Scott getting to his feet and running away, then Slager firing eight shots at the man’s back.

"It is possible for something to happen in that gap to significantly raise the officer’s perception of risk," Seth Stoughton, a former police officer and criminal law professor at the University of South Carolina

Scott was more than $17,500 behind in child support — more than $18,000 with court fees — and had been in jail three times over the issue. He last paid child support in 2012, court records show, and a bench warrant for his arrest was issued in early 2013. His family has said that he might have run because he was behind on payments again and didn’t want to go back to jail.

Police and Slager’s first lawyer initially said the officer fired in self-defense during a scuffle over his department-issued Taser. Within days of Saturday’s encounter, the eyewitness video surfaced and immediately changed perceptions of what had happened, leading authorities to charge Slager with murder and fire him from the police force he’d worked on for five years.

On Friday, Slager’s mother, Karen Sharpe, told ABC’s "Good Morning America" that she couldn’t believe her son — who loved being an officer and had a baby on the way — would have been involved in the incident. She said she’s taking one day at a time and hasn’t watched the cellphone video that helped bring about Slager’s arrest.

"I just have to let it be and hope God takes care of everybody involved — not only my family but the Scott family because I know they’re grieving just like I’m grieving, so I want them to know that," she said.

There is almost nothing in Slager’s police personnel file to suggest that his superiors considered him a rogue officer capable of murdering a man during a traffic stop. In the community he served, however, people say this reflects what’s wrong with policing today: Officers nearly always get the last word when citizens complain.

"We’ve had through the years numerous similar complaints, and they all seem to be taken lightly and dismissed without any obvious investigation," the Rev. Joseph Darby, vice president of the Charleston branch of the National Association for the Advancement of Colored People, said Thursday.

The mostly black neighborhood where the shooting took place is far from unique, said Melvin Tucker, a former FBI agent and police chief in four southern cities who often testifies in police misconduct cases.

Nationwide, training that pushes pre-emptive action, military experience that creates a warzone mindset, and legal system favoring police in misconduct cases all lead to scenarios where officers see the people they serve as enemies, he said.

"It’s not just training. It’s not just unreasonable fear. It’s not just the warrior mentality. It’s not just court decisions that almost encourage the use of it. It is not just race," Tucker said. "It is all of that."

As a steady crowd left flowers, stuffed animals, notes and protest signs in the empty lot where Scott was shot, many said police in South Carolina’s third-largest city routinely dismiss complaints of petty brutality and harassment, even when eyewitnesses can attest to police misbehavior. The result, they say, is that officers are regarded with a mixture of distrust and fear.

Both Slager, 33, and Scott, 55, were U.S. Coast Guard veterans. Slager had one complaint in his personnel file of excessive force that was ultimately dismissed. Scott had the child support issues and traffic violations. But neither man had a record of violence. Slager consistently earned positive reviews in his five years with the North Charleston Police.

Slager’s attorney, Andy Savage, said Thursday that he’s conducting his own investigation, and that it’s "far too early for us to be saying what we think."

The officer is being held without bond pending an Aug. 21 hearing on a charge of murder that could put him in prison for 30 years to life if convicted.

Slager’s file includes a single excessive use-of-force complaint, from 2013: A man said Slager used his stun gun against him without reason. But Slager was exonerated and the case closed, even though witnesses told The Associated Press that investigators never followed up with them. Police say they are now looking at that case again amid questions by the man tased and eyewitnesses who said authorities never questioned them about it.

"It’s almost impossible to get an agency to do an impartial internal affairs investigation. First of all the investigators doing it are co-workers of the person being investigated. Number two, there’s always the tendency on the part of the departments to believe the officers," Tucker said.

Biesecker reported from Raleigh, North Carolina. Associated Press writer Mitch Weiss in North Charleston, South Carolina, and Jonathan Drew in Raleigh, contributed to this report.