Following the departure of development chief Stefan Knirsch, Audi’s chief’s role in the VW group’s emissions scandal is still being probed, according to media reports.

Rupert Stadler selected Knirsch to succeed Ulrich Hackenberg, who was pushed out in the first round of management departures after the scandal broke a year ago, Bloomberg noted, adding Stadler himself has come under increased scrutiny as investigators seek to untangle the origins of the scandal.

“We made it clear from the start that we don’t spare big names in the probe and will act if it becomes necessary,” Berthold Huber, deputy chairman of the unit’s supervisory board, said in a statement cited by Bloomberg about Knirsch’s departure. No reasons for the executive’s abrupt exit were given.

Bloomberg said Audi had already been implicated in the year-long drama, but on a fairly marginal scale. Aside from the rigging of smaller Volkswagen 1.6- and two-litre diesel engines, US authorities targeted Audi for developing bigger [three-litre] powerplants that don’t comply with diesel regulations. The manufacturer initially rejected the allegations before backtracking. Fixing that issue, encompassing about 85,000 vehicles, remains unresolved even after a settlement for the smaller cars.

A recent report in Der Spiegel, cited by Bloomberg and others, linked Stadler to the crisis and another alleged some executives at the brand were aware of the cheating for almost a decade. The Audi CEO, who has run the brand for close to a decade and was part of former VW group CEO and Audi chairman Martin Winterkorn‘s inner circle, fired back, telling the Rheinische Post newspaper last weekend he was helping the investigation.

Bloomberg noted the engine control software at the heart of the cheating scandal dates back to the late 1990s when Audi engineers developed a feature to reduce noise from diesel engines but at the same time elevated emissions. To determine who will be held accountable for the manipulation, investigators are trying to understand when exactly VW engineers refined that code and turned it into a defeat device.

It added Audi could ill afford the distraction of losing its second development chief in less than a year. With a lack of leadership, the brand threatens to lose a step in developing technology to win new customers. Arch-rivals Mercedes and BMW have both posted bigger gains in sales so far this year, entrenching Audi’s lagging position in the three-way race for the top post in premium-car sales.

“The consequences of this degree of management distraction won’t be visible for a number of years,” Willi Diez, who heads up the Institute for Automotive Economics in Geislingen, Germany, told Bloomberg. “We don’t see any immediate impact on sales volumes, but at some point the products will probably suffer.”

There are conflicting reports about what Stadler knew. Reuters, citing three unnamed sources, reported recently investigators had found no suspicious facts against him but Bloomberg, citing a Der Spiegel report about the same time, said lawyers handling the investigation had spoken to company insiders who pointed fingers at Stadler, alleging the CEO knew about the engine manipulation since 2010. The next day, Sueddeutsche Zeitung said the investigators had discovered e-mail correspondence dating back to 2007 from an Audi engineer who had told a wider group of managers that complying with US nitrogen-oxide thresholds wouldn’t be entirely possible without cheating.

Citing unnamed sources, Bloomberg added that Stadler was questioned on 21 September by lawyers from Jones Day, the law firm hired by the carmaker to help investigate the cheating. Members of the supervisory board were briefed on the status of the investigation last Friday and, for now, are satisfied with the explanation they received regarding Stadler’s role in the scandal.

“Audi stabilises the Volkswagen group with its profits,” Stefan Bratzel, director of the Centre of Automotive Management at the University of Applied Sciences in Bergisch Gladbach, Germany, told Bloomberg. “Audi can’t be allowed to wobble.”