BERKELEY, Mo. - A crowd of about 200-300 people gathered outside of a gas station in north St. Louis County overnight after a Berkeley police officer shot and killed an armed 18-year-old.

According to Sgt. Brian Schellman, a spokesman with the St. Louis County Police Department, the shooting took place at 11:15 p.m. at the Mobil station in the 6800 block of N. Hanley Road.

The officer was responding to a reported theft at the gas station when he noticed two young men along the side of the building. As the officer walked toward the front door, one of those men pulled out a handgun and pointed it at the officer, Schellman said.

The officer opened fire, striking the armed individual, identified as Antonio Martin, who died at the scene. The second man ran off.

St. Louis County Police Chief Jon Belmar said the officer is believed to have fired three shots: one struck the armed teen, another struck the front tire on the officer's vehicle, and the third bullet has not yet been accounted for. Martin is not believed to have fired his weapon.

The officer involved in the shooting was assigned a body cam at roll call at the start of his shift, but it was handed off to him later in his shift. He didn't immediately put it on and he was not wearing it at the time of the shooting, Belmar said. The police vehicle was equipped with a dashboard camera, but authorities are unsure if it was activated. Those cameras are typically activated if the officer's lights atop the vehicle are switched on.

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Antonio Martin had a criminal record, including arrests for armed robbery, armed criminal action, and unlawful use of a weapon, and was known to local police departments, Belmar said.Investigators recovered a 9mm handgun at the scene. The weapon was "defaced," meaning the serial number was unreadable. Belmar suspects the serial number was intentionally removed.

Meanwhile, the officer involved in the shooting, a six-year veteran of the Berkeley police force, has been placed on administrative leave.

"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. "So there are no winners here."

A woman at the scene, identified as Toni Martin, claimed to be the 18-year-old's mother. She said her son did not have a gun and had only just left their home to go see his girlfriend.

Crowds began assembling at the gas station shortly after the shooting. NewsChannel 5 reporter John Henry said the crowds were relatively calm until sometime after 2 a.m., when some individuals began throwing rocks and bricks in the direction of police. Chief Belmar said members of the crowd deployed fireworks or some other small explosive devices.

One officer suffered lower leg injuries while trying to get away from the fireworks, Belmar said. A St. Ann police officer was hit by a rock or brick and taken to the hospital.

A man set a small fire inside a QuikTrip store located across the street from the Mobil station. The fire was extinguished in quick fashion, Belmar said.

The St. Louis County Police Department is handling the investigation.

Berkeley, Missouri is a neighboring city to Ferguson, where 18-year-old Michael Brown was shot and killed by a police officer in August 2014, sparking months of civil unrest. The Mobil station is about five miles west of where Brown died.

Information from the Associated Press was used in this report.