German prosecutors have charged former Audi CEO Rupert Stadler with fraud in connection with the 2015 diesel emissions scandal that rocked the Volkswagen Group.

Volkswagen has admitted that it rigged millions of diesel engines to cheat on emissions tests.

Software applications, known as "defeat devices," were installed so that engines produced fewer toxic emissions in a test environment than in normal driving conditions.

Prosecutors said Wednesday that Stadler knew about the manipulation of diesel engine emissions but failed to prevent hundreds of thousands of cars with rigged software from being sold.

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The charges relate to nearly 435,000 Audis, Porsche and Volkswagen cars destined for the US and European markets.

In a statement, Audi said "Our company continues to cooperate fully with the investigating authorities in order to clarify the circumstances that led to the diesel crisis. This clarification is a prerequisite for the successful new start." "The presumption of innocence continues to apply to all defendants until the allegations have been clarified," the statement said.

Stadler had worked for Volkswagen since 1990 before he was arrested in June 2018 in connection with the diesel scandal.

The executive, who was appointed to Volkswagen's management board in 2010, was dumped as Audi's CEO last October after spending several months in jail.

The diesel scandal trashed confidence among consumers and regulators in diesel technology, and cost Volkswagen more than $30 billion in recalls, legal penalties and settlements.

US prosecutors have alleged that the emissions scheme went on for nearly a decade.

They have said that Volkswagen engineers in Germany knew in 2006 the company's new 2.0 liter diesel engine was not capable of meeting emissions regulations.

Instead of going back to the drawing board, they designed the software function that allowed cars to detect when their emissions were being tested, and to boost performance during that time.

In April, German prosecutors charged former Volkswagen chief executive Martin Winterkorn with fraud over diesel emissions. He was also charged with embezzlement and violating competition law.

Winterkorn was also indicted by US federal prosecutors in 2018 on charges of wire fraud and conspiracy. He was accused of defrauding Volkswagen's American customers and violating the Clean Air Act.

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