Rather, the Stuttgart probe is looking into whether as members of Porsche SE's board they withheld information from investors about an unfolding USA investigation into the manipulation before it became public in 2015, causing Volkswagen's shares to drop and exposing shareholders to big losses.
Bloomberg reports that German prosecutors have opened an investigation into whether Müller should have been quicker to notify shareholders of Porsche SE, the holding company that owns the biggest stake in VW Group, about the scandal.
Executives are expected to update investors as soon as price sensitive information comes to light or they will risk accusations of market manipulation.
Not only Matthias Muller but also other top management officials like Hans Dieter Potsch, the chairman of Volkswagen's supervisory board and Martin Winterkorn, the automaker's former chief executive is also in the list of accused who would be interrogated in this scandal.
The inquiry is similar to one launched by prosecutors past year in Braunschweig, near VW's VOWG_p, .DE Wolfsburg headquarters, into current and former VW board members over whether they delayed the release of information about the cheating of diesel emissions tests.
The Porsche holding company is distinct from Porsche sports vehicle brand, which is now part of Volkswagen itself.
Volkswagen faces an array of legal challenges in Germany and worldwide relating to its software, created to fool regulatory nitrogen oxide emissions tests. Seven Volkswagen executives have been criminally charged in the U.S. The company also faces investor lawsuits in Germany alleging it did not inform shareholders of the scandal quickly enough.
FILE - In this March 14, 2017 file photo Matthias Mueller, CEO of Volkswagen addresses the media a press conference of the German Volkswagen company in Wolfsburg, Germany.