Volkswagen AG has decided to seek damages from two former top executives, alleging breaches of duty in the diesel-emissions scandal that’s cost the carmaker more than 30 billion euros (US$35 billion).

An investigation VW billed as the most extensive and costly in German history found failures of duty by Martin Winterkorn, the chief executive officer of the group at the time the crisis erupted, and Rupert Stadler, then the head of the Audi division, the company said in a statement Friday.

Winterkorn, 73, failed to explain the background of VW’s use of impermissible software that enabled certain diesel engines to cheat emissions tests, and didn’t ensure questions raised by U.S. authorities were answered promptly, truthfully and completely, according to the company.

Stadler, 58, failed to ensure that Audi examined whether diesel engines that it developed had used forbidden software functions, VW said. The two CEOs have denied wrongdoing related to the scandal that came to light in September 2015 when U.S. authorities uncovered VW’s use of defeat devices in millions of diesel cars.

The U.S. has charged Winterkorn with conspiracy and wire fraud, but Germany doesn’t extradite its citizens. Investigations in Germany into the roots of the scandal and the people responsible for it have progressed at a slower pace.

Both Winterkorn and Stadler now also face criminal charges in German courts. The start of hearings in the German city of Braunschweig involving Winterkorn and other former VW managers was pushed back to September due to the pandemic. Separate hearings against Stadler and other former Audi officials started in Munich last September and are likely to drag on for years.

VW has shed little light so far on findings of internal investigations as well as an external probe by law firm Jones Day that was commissioned by the supervisory board. The most comprehensive documentation of the manipulation that stretched almost a decade is the plea agreement VW signed with the U.S. Justice Department four years ago.