A federal grand jury in Detroit on Thursday indicted four former executives at Audi over their alleged involvement in the Volkswagen Group's diesel emissions cheating scandal, according to court documents obtained by Bloomberg.

They include Richard Bauder, Axel Eiser, Stefan Knirsch and Carsten Nagel, all of whom were involved in engine development and certification at Audi. All are believed to be in Germany, which doesn't have an extradition agreement with the United States.

The four have been accused of conspiring with Giovanni Pamio, another former Audi exec who was indicted in 2017 over allegations he gave the orders to develop the so-called “defeat device” software used to hide a vehicle's true diesel emissions during tests run by regulators. Their charges include defrauding the U.S., committing wire fraud and violating the Clean Air Act.

The latest indictments come just months after Audi last October paid a $927 million fine over the diesel scandal to settle a German investigation into the matter. The investigation saw former Audi CEO Rupert Stadler initially arrested last June, though he was released the following October and remains under investigation.

The fallout from dieselgate has so far cost the VW Group and its brands $31 billion in buybacks, fixes, and fines in Europe and North America.

While a number a number of individuals have been charged, including former VW Group CEO Martin Winterkorn, so far only two have received prison terms, in both cases in the U.S.. They include Oliver Schmidt who in 2017 received a seven-year prison sentence, and James Liang who that same year received a four-year sentence.