Police chief said officer who fatally shot black teenager Antonio Martin in St Louis suburb had been in ‘imminent danger’ and used ‘what he felt was appropriate force’

Toni Martin, cries out as she talks to police at the scene where she says her son was fatally shot Tuesday at a gas station in Missouri. Photograph: David Carson/AP

St Louis police have released a surveillance video of the final secondsbefore a black teenager was shot on Tuesday night, saying it shows the moment when the teen raised and pointed a handgun at the officer, who then killed him.

The city was disrupted by a protest that went into the early hours of Wednesday morning. Officers used pepper spray and several makeshift explosives were discharged from within the crowd.

Jon Belmar, chief of the St Louis county police, released the video at a press conference hours afterwards in the hope of defusing the tension. Describing the sequence of events at a gas station in Berkeley, a suburb of St Louis, he said that the officer had been in “imminent danger” and had used “what he felt was appropriate force at that time” by firing at the suspect across the hood of the car.

He said the officer fired probably three shots, one of which hit the suspect, one the front tire of his vehicle. As he shot, he stumbled backwards and fell. The suspect, Belmar said, appeared not to have discharged the gun he was allegedly pointing.

Though only one surveillance video has been released so far, the gas station is understood to have several cameras mounted at different locations. The police officer, who was acting alone, was also understood to have a body camera and a camera mounted on the dash of his police vehicle, though Belmar indicated neither was recording.

Belmar declined to identify the officer, who he said was a white male aged 34 who has been on the force for six years. He also declined to identify the shot teenager, though local reports have named him as Antonio Martin.

Martin’s death at about 11.15pm on Tuesday occurred just a few miles from Ferguson, where 18-year-old Michael Brown was shot and killed in August sparking nationwide protests. The latest police shooting attracted a crowd of about 300 people to the Mobil gas station where Martin fell, and about 50 officers were called to the scene, some of whom used pepper spray on the people there. On this occasion the Swat team was kept on standby and tear gas and flash bangs were not used – a conscious effort on the part of police, Belmar said, to learn from the lessons of Ferguson.

The police chief said that three “explosive devices” had been let off by individuals in the crowd, which he described as an “amalgam of fireworks that were packaged up and lit. It’s disturbing when it happens directly by a gas pump.”

Two officers were injured in the melee, he said, and there were four arrests.

The video released by police shows two black teens standing in the parking lot of the gas station. One is dressed in a dark coat and pants, the other in a dark coat with white pants and a white hat.

As they walk away from the lot, a police car with its headlights on is seen driving into the parking lot and stopping in front of them. The officer gets out of the car just as the teen wearing the white pants comes up to him.

Belmar said the officer had been called following reports of a theft, though he declined to go into details.

The officer appears to engage the teen with the white pants in conversation, and as he does so the other teenager walks away but then returns and stands in front of the police vehicle’s headlights. At the end of the video the teen with the dark pants appears to hold up his hand and point towards the officer just feet away.

According to police, he was holding a 9mm handgun which was recovered at the scene, with its serial number defaced. Belmar said the defacing of the gun indicated it could have been stolen or contraband.

St Louis police will be hoping that the release of the video, and the evidence that they claim shows that the officer was acting in self-defence at a moment of mortal danger, will defuse the anger that has erupted again in the city and avoid a repetition of the nightly protests that occurred in Ferguson. But on social media the initial response remained sceptical.