German newspaper Bild am Sonntag (subscription required) reported the existence of an internal letter sent in May of 2014 to Volkswagen's senior managers - including CEO Martin Winterkorn - warning about a probe by the EPA into their diesels. The letter was found by Jones Day, the law firm handling Volkswagen's internal investigation. Citing documents from the investigation, Bild said the letter was from an employee known internally as "Winterkorn's fireman".
"It can be assumed that the authorities will investigate VW systems to establish whether Volkswagen has implemented test-recognition software," the letter states.
Later in the weekend, two sources told Reuters that they had knowledge of the letter. But it isn't certain that Winterkorn - one of the managers who got the letter - ever read it. One of the sources goes on to say the letter came from Volkswagen's product quality and safety department.
This letter now calls into question as to when and how much Volkswagen's senior managers knew about the scandal. Volkswagen publicly admitted they cheated emission tests on certain diesel models last September.