Prosecutors said Müller, along with former Volkswagen CEO Martin Winterkorn and current Porsche (porsche.automobil-holding-se) chairman Hans Dieter Poetsch-all on the management board of Volkswagen and the supervisory board at Porsche at the time-knew that US environmental regulators were looking into the auto maker's diesel-emissions months before the issuance of a public "notice of violation" on September 18, 2015.
Porsche SE, which is headquartered in Stuttgart, controls 52.2 percent of VW's voting shares.
Investigators opened the dossier in February, in response to charges levelled by Germany's Federal Financial Supervisory Authority in the summer of 2016.
Executives are expected to update investors as soon as price sensitive information comes to light, or risk accusations of market manipulation.
Prosecutors said they're investigating whether they delayed releasing information about VW's manipulation of software to cheat emissions tests, and its possible financial implications on the holding company.
Porsche SE said the allegations were unfounded, adding it had complied with disclosure rules.
Porsche SE manages the 52% stake in Volkswagen AG held by the heirs of Beetle inventor Ferdinand Porsche since sports vehicle maker Porsche AG was folded into Volkswagen in 2012.
Volkswagen faces an array of legal challenges in Germany and worldwide relating to its software, created to fool regulatory nitrogen oxide emissions tests.
The key issue at stake is whether the executives knew about the emissions scandal unfolding in the U.S., but failed to inform the stock market in a timely manner. Volkswagen says it met its duties.
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.