Berkeley - The mayor of a St Louis suburb urged for calm on Wednesday after a white police officer killed a black 18-year-old who police said pointed a gun at him, reigniting tensions that have lingered since the death of Michael Brown in nearby Ferguson.A crowd of about 300 people gathered at the gas station where Antonio Martin was shot late on Tuesday, throwing rocks and bricks in a scene reminiscent of the sometimes-violent protests that followed Brown's death.But unlike the shooting of Brown, which was not captured on video, Berkeley Mayor Theodore Hoskins said surveillance footage appeared to show Martin pulling a gun on the unidentified 34-year-old officer who questioned him and another man about a theft at a convenience store. Brown was unarmed."You couldn't even compare this with Ferguson or the Garner case in New York," Hoskins said, referring to the chokehold death of Eric Garner, another black man killed by a white police officer.He also noted that unlike in Ferguson, where a mostly white police force serves a mostly black community, more than half of the officers in his city of 9 000 are black, including top command staff.St Louis County Police Chief Jon Belmar did not provide more details about the theft Martin was being asked about. He said Martin pulled a loaded 9mm handgun and the officer fired three shots while stumbling backward. One hit Martin, who didn't fire his own gun. He died at the scene."I don't know why the guy didn't get a shot off, whether his gun jammed or he couldn't get the safety off," said attorney Brian Millikan, who is representing the officer. He said that the officer was lucky to be alive and certain he had no choice but to use lethal force.OldestSt Louis County police and the city of Berkeley are investigating the shooting, which Belmar called a tragedy for both Martin's family and the officer, who has been on the force for six years."He will carry the weight of this for the rest of his life, certainly for the rest of his career," Belmar said of the officer. "There are no winners here."The officer wasn't wearing his body camera, and his cruiser's dashboard camera was not activated because the car's emergency lights were not on, Belmar said.Police released surveillance video clips from three different angles. The men can be seen leaving the store as a patrol car drives up. The officer gets out and speaks with them.About 90 seconds later, one appears to raise his arm, though it's difficult to see what he's holding because they were several feet from the camera. Belmar said it was a 9mm handgun with one round in the chamber and five more in the magazine.Police were searching on Wednesday for the other man, who ran away.Belmar said Martin had a criminal record that included three assault charges, plus charges of armed robbery, armed criminal action and unlawful use of a weapon.Phone messages left for his parents were not returned. His mother, Toni Martin-Green, told the St Louis Post-Dispatch that Antonio was the oldest of four children."He's like any other kid who had dreams or hopes," she said. "We loved being around him. He'd push a smile out of you."His was the third fatal shooting of a young black man by a white police officer in the St Louis area since Brown was killed by Ferguson officer Darren Wilson on 9 August. Kajieme Powell, aged 25, was killed on 19 August after approaching St Louis officers with a knife. Vonderrit Myers, aged 18, was fatally shot on 8 October after allegedly shooting at a St Louis officer.Each killing has led to protests, as did a grand jury's decision last month not to charge Wilson in Brown's death. A crowd quickly gathered late on Tuesday in Berkeley. The demonstration involving about 300 people turned violent.More than 50 police officers responded to protests on Tuesday. Belmar said officers used pepper spray but not tear gas. Four people were arrested on charges of assaulting officers.