DETROIT (AP) — A federal grand jury in Detroit has indicted former Volkswagen CEO Martin Winterkorn on charges stemming from the company's diesel emissions cheating scandal.

The four-count indictment unsealed Thursday alleges that the automaker's top executive at the time knew about the plot.

The 70-year-old Winterkorn is charged with three counts of wire fraud and one of conspiring to violate the Clean Air Act. He was indicted in March.

Volkswagen has admitted to programming its diesel engines to activate pollution controls when being tested in government labs and turning them off when on the road.

The U.S. government believes Winterkorn is in Germany, so it's unlikely he'll ever see a U.S. courtroom or jail. Germany does not typically allow extradition of its citizens to other countries.