German prosecutors say they've opened an investigation of former Volkswagen CEO Martin Winterkorn on allegations of market manipulation in connection with the company's scandal over cars rigged to cheat on U.S. diesel emissions tests.

Braunschweig prosecutor's spokesman Matthias Diekman said in a statement Monday that Winterkorn and one other, unidentified, VW employee are being investigated on allegations they did not release information about the manipulation in a timely manner. They opened the investigation at the behest of Germany's Federal Financial Supervisory Authority.

Volkswagen did not answer telephone calls seeking comment.

Winterkorn stepped down as the scandal came to light, saying he was doing so "in the interests of the company even though I am not aware of any wrongdoing on my part."