German prosecutors open investigation into ex-Volkswagen CEO Martin Winterkorn

FILE - In a Tuesday, May 5, 2015 file photo, Volkswagen CEO Martin Winterkorn addresses the shareholders during the annual shareholder meeting of the car manufacturer Volkswagen in Hannover, Germany. Winterkorn apologized Sunday, Sept. 20, 2015, after the Environmental Protection Agency said the German automaker skirted clean air rules by rigging emissions tests for about 500,000 diesel cars. "I personally am deeply sorry that we have broken the trust of our customers and the public," Volkswagen chief Martin Winterkorn said in a statement. (AP Photo/Frank Augstein, File)

BERLIN -- German prosecutors on Monday opened an investigation against former Volkswagen CEO Martin Winterkorn to establish what his role was in the emissions-rigging scandal that has shaken the world's largest automaker.

The investigation will concentrate on the suspicion of fraud committed through the sale of vehicles with manipulated emissions data, and aims to determine who was responsible, prosecutors in Braunschweig said in a statement.

In the German system, anyone can file a criminal complaint with prosecutors, who are then obliged to examine it and decide whether there is enough evidence to open a formal investigation.

In this case, following the revelations about the rigged tests, prosecutors in Braunschweig, near VW's headquarters in Wolfsburg, received about a dozen complaints, including one from Volkswagen itself, said spokeswoman Julia Meyer.

She said it was too early to say if and when prosecutors may try and interview Winterkorn himself, and that she did not know whether he already had an attorney to represent him.

She said at this stage, she could not estimate how long the investigation would last.

FILE - In a Tuesday, May 5, 2015 file photo, Volkswagen CEO Martin Winterkorn addresses the shareholders during the annual shareholder meeting of the car manufacturer Volkswagen in Hannover, Germany. Winterkorn apologized Sunday, Sept. 20, 2015, after the Environmental Protection Agency said the German automaker skirted clean air rules by rigging emissions tests for about 500,000 diesel cars. "I personally am deeply sorry that we have broken the trust of our customers and the public," Volkswagen chief Martin Winterkorn said in a statement. (AP Photo/Frank Augstein, File)

"This is a very broad case and in other such investigations it has taken many months, sometimes years," she said.

Winterkorn, Volkswagen's CEO since 2007, resigned Wednesday - days after the world's top-selling carmaker admitted that it had rigged diesel emissions to pass U.S. tests during his tenure. He said that he was going "in the interests of the company even though I am not aware of any wrongdoing on my part."

Under German law, it is not possible to bring charges against a company, only against individuals. Meyer would not elaborate on specifics of the investigation, and it wasn't clear what Winterkorn's suspected role might be. There was no immediate comment from Volkswagen on the prosecutors' decision.

Fraud can carry a prison sentence of up to 10 years in Germany.

The head of VW's Porsche division, Matthias Mueller, was appointed Friday as Volkswagen's new CEO. He promised to do everything to win back the public's trust.

The company has admitted that it used a piece of engine software to cheat on diesel car emissions tests in the U.S. It will have to fix programming it has said is in some 11 million cars worldwide, far more than the 482,000 originally identified by U.S. authorities.

Details on what cars are involved have emerged gradually. The group, which has 12 marques in all, said Friday that some 5 million cars made by its core Volkswagen brand had the diesel engine in question.

On Monday, Audi said that 2.1 million of its vehicles also had the engine, while Czech-based Skoda said 1.2 million vehicles were affected.

Volkswagen shares, which were pummelled early last week before recovering some ground, headed south again on Monday. They were down 7.1 percent in afternoon Frankfurt trading at 107.40 euros ($120.20).

Read more about Volkswagen's diesel emissions scandal