On Wednesday afternoon, Volkswagen Group said that the head of the US branch of the company, Michael Horn, will be stepping down to "pursue other opportunities immediately,” according to The Wall Street Journal.

Horn led Volkswagen’s US operations since January 2014, and his departure comes as VW Group is under extreme scrutiny for building its cars with "defeat devices,” or software on the car’s engine management system that disables the car’s emissions control system when it's driving under normal conditions but enables the emissions control system when the car has to pass laboratory testing.

Volkswagen said Horn’s resignation decision was reached in "mutual agreement.” Hinrich J. Woebcken, a Volkswagen Group chairman and the head of VW’s North America operations, will lead the US division in the interim.

Horn is not currently a suspect in any of the ongoing investigations probing VW’s emissions scandal. The company has maintained that senior management never knew of the decision to update Volkswagen, Audi, and Porsche diesel vehicles with software that would run afoul of US emissions regulations. The automaker also claimed that VW Group’s CEO at the time, Martin Winterkorn, only learned about the gravity of the situation a month before the US Environmental Protection Agency (EPA) publicly announced that it was serving VW a Notice of Violation in September 2015.

The New York Times notes that Horn’s tenure was marked by his efforts to reestablish good relations between Volkswagen Group and the network of VW dealers on the ground in the US. The paper suggested that Horn’s departure "might signal more modest ambitions in the United States” for VW Group. Volkswagen was recently sued for tens of billions of dollars by the US Justice Department for placing illegal software on cars it sold in the US.

Earlier this week, German prosecutors said they were expanding their investigation of the emissions scandal to include 17 additional Volkswagen employees on top of the original six employees they brought in for questioning. German law protects the identities of the suspects, but the prosecutors said that so far, no management personnel were being scrutinized.

Currently the company is in negotiations with the EPA and California’s Air Resources Board (CARB) to find a way to resolve the fact that nearly 600,000 VW diesel vehicles are being driven on US roads emitting substantially more nitrogen oxide (NO x ) than is legally permitted. CARB, with the EPA’s blessing, has already rejected one proposal that VW put forward. On Tuesday, the chief of CARB’s enforcement division, Todd Sax, told state legislators that it “may not be possible” to fix VW’s diesels to the point where they are road-certifiable.

"We will have to decide what the best approach is to dealing with these vehicles, and one of the options potentially would be to accept something less than a full fix,” Sax said, according to Reuters.

Sax’s comments seemed to be positive for VW Group, suggesting that the automaker might be permitted to allow the existing polluting cars to remain on the road, while paying the state in fines to mitigate the environmental harm those cars are causing. Volkswagen’s worse-case scenario involves being forced to buy back the diesel vehicles with defeat devices from its customers, a course of action that a German newspaper reported that Volkswagen was coming to terms with earlier this year.