In November 2015 Audi admitted installing emissions defeat devices in its cars, and Audi's been pegged in several reports as the source of the initial defeat software responsible for Dieselgate. At the end of May, authorities named Stadler and Audi board member Bernd Martens as two key suspects among 18 being investigated in the emissions investigation. In early June, Munich prosecutors summoned Stadler to answer questions alongside ex-VW Group CEO Martin Winterkorn, former Audi technical director Ulrich Hackenberg, and other Group execs concerning the emissions investigation.
Not long after that, investigators searched Stadler's and Martens' homes. Martens, who is also Audi's head of procurement, is said to have run a task force coordinating Audi's Dieselgate response with the Volkswagen Group. Apparently, based on the questioning and evidence found during the raids, one week ago investigators accused Stadler of fraud and falsification of documents that allowed the company to sell illegal diesels. Prosecutors have accused Stadler of being involved in controverting emissions regulations since 2012.
Audi's problems on the ground aren't over yet, either. In May, the carmaker admitted to German regulators that roughly 60,000 A6 and A7 sedans had emissions software irregularities, using a different software than the one responsible for Dieselgate.
Munich prosecutors are questioning Stadler during what is called "investigative detention," and the VW board will meet today to discuss the development. With Audi having made the largest contributions to VW's profits, and with the CEO having stayed out of the criminal fray, Stadler had such strong support from the Porsche and Piech families that he got a new five-year contract in May 2017. An Audi statement on the arrest said, "For Mr. Stadler, the presumption of innocence continues to apply." It's not clear if his status as CEO will do the same, since Stadler figured in VW Group CEO Herbert Diess' plans to reorganize company leadership.
The last high-ranking Audi exec taken into custody was Wolfgang Hatz, the brand's former head of engine development. He's been in jail since September 2017.