BERKELEY, Mo. (AP) -- Violent protests broke out in suburban St. Louis after another black 18-year-old was fatally shot by a white police officer. St. Louis County Police Chief Jon Belmar said the officer was questioning the 18-year-old and another man about a theft late Tuesday at a convenience store in Berkeley when the young man pulled a 9mm handgun on him. The officer stumbled backward but fired three shots, one of which struck the victim, Belmar said. Police released surveillance video (below) that captured much of what transpired before the officer fired. Watch the upper right-hand corner of the frame as the police car pulls up and an officer gets out to talk with the young men. At around the 1:35 mark, one of the men steps back, turns, then holds out an object with his arm extended, pointing in the officer's direction.That's where the video stops. Berkeley is just a few miles from Ferguson, where a white police officer fatally shot Michael Brown, an unarmed black 18-year-old, on Aug. 9. Brown's death sparked weeks of sometimes violent demonstrations and a grand jury's decision to not charge Officer Darren Wilson in the shooting has spurred a nationwide movement to protest police brutality. Belmar declined to name the 18-year-old killed in Berkeley, but a woman at the scene told reporters she was his mother and identified him as Antonio Martin. Belmar said he was 18 years old and black. The 34-year-old white police officer, a six-year veteran of the Berkeley Police Department, is on administrative leave pending an investigation, Belmar said. "He will carry the weight of this for the rest of his life, certainly for the rest of his career," Belmar said. "So there are no winners here." Police released surveillance video from the parking lot outside the store. The nearly two-minute clip shows two young men leaving the store at about the time a police car rolls up. The officer gets out and speaks with them. About a minute-and-a-half later, the video appears to show one of the men raising his arm, though what he is holding is difficult to see because they were several feet from the camera. Belmar said it was a 9mm handgun. The other man ran away, and police are searching for him.