German prosecutors have reportedly opened an investigation into the former Volkswagen CEO Martin Winterkorn.
Mr Winterkorn resigned last week saying he was "shocked" by revelations that the German carmaker had cheated emissions tests in the US.
He had been in charge of the car giant since 2007, and said he was "clearing the way for a fresh start" by standing aside.
According to The Associated Press, 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 them 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.
When he resigned, Mr Winterkorn said: "I am shocked by events of the past few days. Above all, I am stunned that misconduct on such a scale was possible in Volkswagen Group."
Volkswagen admitted on Friday that it had been rigging emissions tests to comply with regulations since 2009.
As many as 11 million vehicles worldwide could have been fitted with so-called "cheat switches" that mask the true level of emissions they emit during tests.
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