On Thursday, Wolfgang Hatz, former engine chief for Volkswagen and Audi and later the head of research and development at Porsche, was arrested in Munich. With Hatz's arrest, the slow-moving investigations of Volkswagen Group in the aftermath of the 2015 emissions scandal seem to be gathering momentum, according to reports from German paper Süddeutsche Zeitung and the New York Times.

The news comes by way of anonymous sources, as German privacy law prohibits the government from disclosing the identities of suspects. German authorities confirmed to the New York Times that a suspect was arraigned on Thursday morning in connection with the ongoing investigation of VW Group’s Audi unit.

Hatz was the engine chief at Audi between 2001 and 2007, right around the time that the company began implementing a software-based “acoustic condition” workaround for its diesel engines. According to court filings and academic research, Audi allegedly wanted to get rid of the rattling noise that some diesel engines make on startup, so it created software to inject extra fuel into the engine on ignition. The company then worked to mask the extra emissions created by this fix, and from there, the emissions cheating software apparently grew as the company demanded different and increasingly hard-to-achieve features for its diesel engines. There’s evidence that the Audi software was then borrowed by Volkswagen for its line of diesels, which were aggressively marketed as “clean diesel cars” in the US.

After 2007, Hatz moved to become the engine chief at sister company Volkswagen, “where he reported directly to the management board” according to the Times. In 2011, he moved on to another sister company, Porsche, where he led research and development until he was suspended by the company after the diesel scandal broke in the US after 2015.

Hatz, who is reportedly being held without bail, is the fourth VW Group employee to be arrested in connection with the scandal (VW Group as an entity pleaded guilty to violating the Clean Air Act in early 2017). James Liang, a former VW engineer, was arrested in 2016 in the US and sentenced to 40 months in prison; Oliver Schmidt, a German emissions compliance executive who worked in the US, was arrested in Miami in December; and Zaccheo Giovanni Pamio, an Italian citizen who was the former chief of thermodynamics in Audi’s engine development department, was arrested in Germany earlier this year.

Hatz was not among the six VW Group executives that the US Department of Justice indicted earlier this year. According to the Times, Hatz’s arrest indicates that German officials are wrapping up their investigations of the company and may start to make more arrests more rapidly in the coming months. The paper reports that German investigations “include three past or current members of top management: Hans Dieter Pötsch, the chairman of the Volkswagen supervisory board; Herbert Diess, the head of the unit that makes Volkswagen brand cars; and Martin Winterkorn, a former chief executive.”

At a company-wide level, the German auto group is hitting some more rough road despite its efforts to wrap up investigations and shift to electric vehicles. Although Volkswagen has agreed to around $27 billion in settlements with various stakeholders in the US, just today it announced that it would have to take another $2.9 billion charge related to the scandal. Executives explained that the company would have to set aside the billions to cover expenses related to unexpected difficulties in fixing some 600,000 affected diesel cars in the US, according to Reuters. Under settlement terms, VW Group must fix those cars that are not in compliance with US federal emissions standards. The cars must be fixed even if VW Group intends to sell them in other markets where emissions standards are more relaxed.