Google has monopolized the technology used to buy and sell online display ads by restricting or eliminating the choices of its customers — both website publishers and advertisers — the US Justice Department alleged at a federal antitrust trial.

Google has opened its defense against allegations that it holds an illegal monopoly on online advertising technology with witness testimony saying the industry is vastly more complex and competitive than portrayed by the federal government.

As the government wraps up its case, it has built a picture of how Google has become dominant among companies that buy and sell ads online.

Lawyers for the government have revealed damning Google correspondence and called witnesses who describe anti-competitive practices. Google, however, says ‘there is no monopoly power.’

The U.S. government’s antitrust suit against Google’s (NASDAQ:GOOG) (NASDAQ:GOOGL) advertising business features the company’s internal emails as what prosecutors describe as key evidence that executives were aware of its dominance in the online ad market,