An inquiry hears that the police officer who killed Azelle Rodney had shot dead two other people during his career.
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Mr Rodney, 24, was gunned down by the officer, identified only as E7, after the car in which he was travelling was stopped by police in Edgware, north London in April 2005.
The police team believed he was part of an armed gang who were on their way to rob drug dealers.
The inquiry into Mr Rodney's death heard that during an incident in the 1980s E7 shot two men and injured another two.
Inquests into the men's deaths later found that they had been lawfully killed, and the officer received a commendation from the Metropolitan Police Commissioner for his conduct.
The two injured men were later tried and jailed.
An inquiry is being held into Mr Rodney's death instead of an inquest because of sensitive information that would have to be withheld from a coroner.
'Words of advice'
The hearing was told that E7 received a commander's commendation in the 1990s after an armed stand-off with a gunman in a minicab office. He said: "I could tell that his heart wasn't in it and I screamed 'armed police' at him and the man dropped the gun when I was just about to open fire."
In 2004, police watchdog the Independent Police Complaints Commission (IPPC) recommended that he was given "words of advice" after an armed operation. It was claimed that he left a police car without permission during the operation to test his radio and buy coffee.
E7 said his superiors thought it was "a storm in a teacup" and did not give him advice. A man was killed during the operation but the officer was not directly involved.
He said: "Nothing I did delayed us getting to the scene at all."
The officer was arrested after a drunken brawl at a nightclub in Covent Garden, central London, in December 2000, which he admitted was "not one of my proudest moments".
"I ended up with about four or five bouncers on top of me and I ended up in a fight," he told the inquiry. "My warrant card was ripped off me and thrown away.
"We all do silly things occasionally when we drink but I was old enough and wise enough to know better. It was one of those situations that got out of hand."
18 rounds per second
On the day Mr Rodney was killed - April 30 - E7 said he was concerned that the three men in the car might have a sub-machine gun.
The VW Golf in which they were travelling was under surveillance for several hours before it was brought to a stop, and E7 opened fire within a second of pulling up beside the car.
He said they feared the gang had "a fairly compact weapon that could fire in excess of 1,000 rounds a minute, that's 18 rounds per second".
E7 went on: "The reality is that these people would be untrained, and actually an untrained person with a high-capacity, high-repetition sub-machine gun is more dangerous than a trained person."
The officer, who was first firearms trained in the early 1980s, tried putting a ballistic shield in the car he was using, but it blocked access to the door handle.
When asked why he had done this, he said: "I was the person that was going to be right next to someone with a sub-machine gun.
"It wasn't the first time that we had confronted dangerous people armed with that type of weaponry.
"This was high on the scale of danger but it was certainly no more dangerous than other operations that we'd carried out over the years."
The officer has been granted anonymity during the public inquiry, and members of the press were banned from the courtroom as he gave evidence, listening to audio feed from a separate room.