A spokesman for the prosecutor's office in Braunschweig, near Volkswagen's headquarters, said there was an initial suspicion of attempted obstruction of justice and concealment of evidence. Volkswagen (VLKAY) declined to comment on an ongoing investigation. Volkswagen admitted on Sept. 18 it had cheated the Californian environmental tests, knocking a fifth off its market value, causing its chief executive to resign and potentially costing it billions in court cases, fines, and technical fixes. Soon afterwards, it ordered law firm Jones Day to carry out an independent internal inquiry over the matter. Get Data Sheet, Fortune's daily technology newsletter. Some investors are suing Volkswagen for not having informed the market in a timely manner of its huge impending problem. British law firm Slater & Gordon said it had been "inundated" by customers looking to bring a group action against Volkswagen if it is found that they suffered loss by installation of the defeat device.