Azelle Rodney, 24, was killed in Mill Hill, north London, in April 2005, the Old Bailey heard.
Anthony Long opened fire on Mr Rodney after his police car pulled up in an operation to foil an attempted robbery.
Mr Long, who says he believed his colleagues were in "imminent" danger, denies murder.
A jury has retired to consider its verdict in the trial of a police marksman who shot and killed a suspected armed robber 10 years ago.