German prosecutors have extended a probe into Volkswagen's use of "defeat device" software in diesel cars to former CEO Martin Winterkorn.

Winterkorn, who resigned shortly after the existence of VW "defeat device" software was revealed by the EPA, has said he had no knowledge of the emissions-manipulating software until shortly before the scandal broke.

This is the first time prosecutors in Volkswagen's home country have named Winterkorn in the investigation of the software, which was used to cheat on emissions tests.

DON'T MISS: VW settles diesel cheating cases: felony pleas, $4.3 billion fines

However, he was previously tied to a separate probe of market manipulation related to the diesel scandal, along with other VW executives.

Winterkorn is one of 37 people now being investigated as part of the diesel probe, which is 16 more than was previously acknowledged, according to Bloomberg.

Investigators raided more than two dozen locations this week in connection with the probe, prosecutors in Braunschweig, Germany, said in a statement released Friday.

2015 Volkswagen Golf TDI

2015 Volkswagen Golf TDI

Winterkorn's home and office in Munich were among the locations raided, according to German newspaper Bild.

Braunschweig prosecutors opened their investigation into Volkswagen defeat device software shortly after the EPA announcement of its existence in September 2015.

Prosecutors previously acknowledged investigating 21 individuals, none of whom were top VW executives.

MORE: 5 more VW diesel execs indicted, including R&D head, after weekend arrest

Last week, in his public appearance since resigning 16 months ago, Winterkorn told German lawmakers in Berlin that he was unaware of the existence of the "defeat device" software until shortly before the scandal broke.

"It's incomprehensible why I wasn't informed early and clearly," Winterkorn told a parliamentary committee, adding that, had he known, he would have "prevented any type of deception or misleading of authorities," according to a separate Bloomberg report on the meeting.

Winterkorn's role in the deployment of the "defeat device" software is the subject of much speculation, but no one knows for sure.

2010 Volkswagen Golf TDI

2010 Volkswagen Golf TDI

Investors are suing Volkswagen in Germany for a combined $8.6 billion, alleging the automaker did not report the U.S. regulatory probe into its emissions-cheating software promptly enough.

That case rests on exactly when top VW executives knew of the existence of the software, and that it constituted a violation of regulations.

Volkswagen recently settled with the U.S. Justice Department, agreeing to plead guilty to criminal charges and pay $4.3 billion in fines.

The Justice Department indicted six VW executives and arrested one, Oliver Schmidt, who was apprehended in Miami while returning to Germany from a vacation.


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