Frank Barry, 29, turned vigilante after being beaten up, threatened and robbed in the street, David Spens for the prosecution said at the Old Bailey. He said he tracked down Tyron Harding, who he believed to be the culprit, and shot him three times.
Mr Barry made a complaint at a police station last June but police did not proceed with the allegation, the jury was told.
Mr Barry, of south-west London, denies attempted murder, causing grievous bodily harm with intent and possessing a firm.
The trial continues today.