Munich prosecutors have charged four more former Audi executives with fraud, false certification and illegal false advertising for allegedly cheating diesel emissions tests, handelsblad and Reuters reported on Thursday, citing sources familiar with the matter.

The indictment, which targets three former Audi board members and a retired division head, covers a total of 434,420 Audi, Volkswagen and Porsche marques sold mainly in the U.S. and Europe.

The four are accused of promoting the development of an engine operated by illegal software that would allow it to produce lower emissions under test conditions than under normal driving conditions.

The prosecution alleges that the accused former Audi board members repeatedly knew about the cheating between October 2013 and September 2015, but failed to stop it, so that the models were still being sold.

In addition, one of the former board members has been accused of defrauding board members of their pay by keeping quiet about his involvement before he became a board member in 2016.

Since 2015, Audi and its parent Volkswagen Group have admitted to using illegal software to cheat on emissions, which has caused continuing turmoil in the management of Volkswagen Group, including the abrupt departure of former Volkswagen CEO Matthias Muller and the arrest of former Audi CEO Rupert Stadler.

Stadler was arrested at his home in Ingolstadt in June 2018 in connection with the diesel emissions cheating scandal. Stadler and three other defendants were charged in July with fraud, forgery and unlawful false advertising.