Volkswagen ornaments sit in a box in a scrap yard in Berlin, Germany, Wednesday, Sept. 23, 2015. The revelation that Volkswagen rigged diesel-powered cars to emit lower emissions during EPA tests is particularly stunning since Volkswagen has long projected a quirky brand image with an emphasis on being environmentally friendly _ an image that now appears in tatters. (AP Photo/Michael Sohn)
Volkswagen ornaments sit in a box in a scrap yard in Berlin, Germany, Wednesday, Sept. 23, 2015. The revelation that Volkswagen rigged diesel-powered cars to emit lower emissions during EPA tests is particularly stunning since Volkswagen has long projected a quirky brand image with an emphasis on being environmentally friendly _ an image that now appears in tatters. (AP Photo/Michael Sohn)
Olaf Lies, economy and transport minister of VW's home state Lower Saxony, which holds a 20 percent stake in the company, said the investigation into the scandal was only just starting.
"There must be people responsible for allowing the manipulation of emission levels to happen," he said.
Winterkorn said Wednesday he took responsibility for the "irregularities" found by U.S. inspectors in VW's diesel engines, but insisted he had personally done nothing wrong.
VW is filing a criminal complaint with German prosecutors, seeking to identify those responsible for any illegal actions in connection with the scandal.