The magazine’s website, citing unnamed sources, reports that an employee had contacted chief executive Matthias Müller directly in response to the new boss’s declaration that he wanted to investigate past cheating thoroughly. Müller had said he wanted to create a new, more open culture at a company that has been run for the last 25 years by a tight circle of engineers under the patronage of a single family.

According to Wirtschaftswoche, the employee had personally informed Müller of how tests measuring fuel consumption and carbon dioxide emissions were manipulated, albeit while staying within the lax conditions allowed under European testing standards. As Fortune reported earlier today, the company’s shares dropped another 10% after the company acknowledged that it exaggerated the fuel efficiency of some diesel and gasoline models.

In the company’s statement Tuesday, Müller had hinted that his earlier statements about a thorough clean-up had played a role in the new disclosures. “From the start, I have pledged myself to a complete and unsparing investigation of what has happened,” Müller said. “We will not stop for anyone or anything. It’s a painful process but there is no alternative for us.”

Müller’s willingness to open up a whole new can of worms will go some way to answering criticism that he is himself too close to previous management to carry out a truly rigorous investigation. However, there is still a question mark over his own role in the emissions scandal, given that VW’s Porsche unit, which he led until October, has now been accused by the Environmental Protection Agency of installing “defeat devices” on vehicles sold in the U.S..