BERLIN/FRANKFURT -- Investigators looking into Volkswagen Group's diesel-emissions scandal have found no suspicious facts against the head of Audi, three people familiar with the matter said.
Volkswagen CEO Matthias Mueller said on Tuesday that Audi CEO Rupert Stadler had been questioned by U.S. law firm Jones Day but gave no details about the inquiry.
A report by the German Der Spiegel magazine said witnesses inside the company alleged the executive had known about the engine manipulation since 2010.
Audi has admitted its 3.0-liter V-6 diesel engine was fitted with emissions-control software, deemed as illegal in the U.S., where VW's emissions test-rigging scandal broke a year ago.
"So far nothing has been relayed to the company that would suggest to dismiss Mr Stadler," said one of two sources that are close to Audi.
The questioning by Jones Day, tasked by VW last year to investigate the manipulations, has yielded no solid evidence against Stadler, a second source close to Audi said.
VW and Audi declined comment.
VW's supervisory board, meeting in Wolfsburg on Friday, is also discussing the situation with Stadler, one of the sources said.
Stadler has stood at the helm of Audi since 2007 and three years later joined VW Group's nine-member management board.