German prosecutors have opened an investigation into former Volkswagen CEO Martin Winterkorn amid an international scandal over the auto maker’s cheating on diesel emissions tests. Prosecutors will seek to determine who is responsible for the rigged results. Winterkorn denies involvement in the scandal, though Bloomberg News reported last week that the deception was run out of VW headquarters in Wolfsburg. The investigation comes amid Audi’s announcement that the test-cheating device was fitted into 2.1 million of its vehicles. “We’re working at full speed to find a technical solution,” an Audi spokesman said.