Volkswagen's former Chairman Ferdinand Piech, who left the company following a showdown with ex-Chief Executive Martin Winterkorn in 2015, has testified to prosecutors investigating Winterkorn's involvement in the carmaker's diesel scandal, according to Winterkorn's lawyer. "Winterkorn learned a few days ago of the existence of more detailed testimony by the former chairman, Prof. Dr. F. Piech," a lawyer for Winterkorn said in an emailed statement, adding that Winterkorn did not know any details about what Piech told prosecutors.