Associated Press
    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 polite 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