Internal memos and emails from within the VW Group have revealed that top company managers, including former chief executive Martin Winterkorn, knew about potential issues with US emissions regulators in early 2014.

The New York Times reports that Winterkorn received word form a confidant in May 2014 that regulators in the U.S. could accuse the company of installing defeat devices in its diesel vehicles to cheat emissions testing.

Despite this warning, the Volkswagen Group continued to produce its illegal 2.0-liter and 3.0-liter diesel engines until it admitted in September 2015 that over 11 million vehicles worldwide had been installed with devices that recognize when a car is being tested for emissions and activates equipment to temporarily lower emissions.

At the time of Winterkorn’s resignation on September 23, the chief claimed to have only learned about the defeat devices just prior to the company’s public admission.

If it is proven that Volkswagen’s leading executives new of the cheating before September 2015, fines could jump significantly due to their failure to disclose problems that could affect the company’s stock price.

In total, Volkswagen could face fines in excess of $90 billion.

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