St. Louis Police have uploaded to YouTube CCTV footage from the petrol station where Antonio Martin was shot in Berkeley, Missouri.
The video appears to show a man raising a gun at police officers before being shot.
The incident took place near the flashpoint town of Ferguson where teenager Michael Brown was killed by officer Darren Wilson earlier this year.
The teen was reportedly killed outside the Mobil gas station in the town and social media users posted photos and footage of Martin's mother at the scene.
Initial reports from witnesses suggest that Martin was unarmed while others claim that a gun was found at the scene. Clashes have broken out between protesters and police following the shooting.