VW had hired the firm, Jones Day, to complete an internal investigation, but the full findings were never made public.

Volkswagen has cried foul after German prosecutors raided the outside law firm, Jones Day, that handled the company's internal investigation of the emissions scandal.

Officials searched both Jones Day and Audi offices on Wednesday, hinting at an ongoing inquiry aimed at identifying individuals who may have been responsible for the emissions cheat, according to Reuters.

"In our opinion the search of a law firm mandated by a company contravenes the principles of the code of criminal procedure," VW spokesman Eric Felber said in a particularly adversarial statement.

VW initially promised to release findings from the Jones Day probe. The company later backtracked, however, and argued that it must maintain 'confidentiality' as it pursued settlement agreements with US regulators. The statement immediately raised red flags, prompting some investors to push for a wider independent investigation. The group argued that Jones Day was only focusing on lower employees and the management board, potentially shielding the supervisory board.

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German prosecutors are said to be investigating at least 37 workers and executives.