Volkswagen's outgoing CEO, Martin Winterkorn, knew about the company's emissions and fuel economy cheating a full year before they became public knowledge, the German newspaper Bild am Sonntag reports.

The newspaper reports that VW stopped selling the Polo TDI BlueMotion back in spring 2015 because it had discovered that its actual fuel economy was 18 percent below its official rating. At the time, VW claimed that it pulled the Polo because of "subdued demand."

Bild, citing "sources close to Winterkorn," says that Winterkorn knew about this fuel economy discrepancy back in spring 2015. Furthermore, Bild says that VW's top executives knew about fuel economy and emissions issues with its other cars a year ago. Bild did not cite its source for the "year ago" assertion, however. With this scandal likely to cost VW tens of billions of euros in fines and lost revenue, Bild hopefully vetted its sources enough, lest it get hit by a massive defamation suit.

The VW scandal, which began in September, has tumesced into a cock-up of gnarly proportions. First, it looked like just a few hundred thousand diesel vehicles in the US had been fitted with a "defeat device" for cheating on emissions testing. Then the problem spread to Europe and the rest of the world, with the company admitting that around 11 million vehicles had false emissions ratings. More recently, it has emerged that VW was cheating on carbon dioxide emissions and fuel economy, too.

Winterkorn has since stepped down as CEO of Volkswagen Group, replaced by Matthias Müller who was previously CEO of the VW subsidiary Porsche. Ironically, at the beginning of November it emerged that some Porsches were also involved in the emissions imbroglio—Porsches that were produced while Mülller was CEO.

Back in October, VW claimed that the defeat devices had been the work of rogue software engineers, and that the company's execs hadn't been aware of what they were up to. If Bild's report is accurate, that would seemingly throw a rather large spanner in the company's narrative.