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.

The antitrust trial over allegedly monopolistic practices in the $200 billion digital advertising industry could lead to significant changes.

The judge who will decide whether Google holds a monopoly over technology that matches buyers and sellers of online advertising must choose whether to believe what Google executives wrote or what they’ve said on the witness stand.

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.