BERLIN -- German prosecutors raided Volkswagen's headquarters and other offices on Thursday as part of their investigation into the carmaker's rigging of diesel emissions tests.
Prosecutors in Braunschweig, near the company's headquarters in Wolfsburg, said the aim of the searches was to "secure documents and data storage devices" that could identify those involved in the alleged manipulation and explain how it was carried out.
Volkswagen said it was supporting the investigation and had handed over a "comprehensive" range of documents.
Almost three weeks after it confessed publicly to rigging U.S. emissions tests, Europe's largest carmaker is under huge pressure to identify those responsible, fix affected vehicles and clarify exactly how and where the cheating happened.
The biggest business crisis in Volkswagen's 78-year history has wiped more than a third off its share price, forced out its long-time chief executive, prompted investigations across the world and rocked both the car industry and German establishment.
Later on Thursday, the company's top U.S. executive will tell a panel of U.S. lawmakers he knew the carmaker might be breaking U.S. emissions rules as long as 18 months before it admitted cheating diesel tests to regulators.
The admission by Michael Horn, in a written testimony to a congressional oversight panel a day ahead of the hearing, is likely to raise questions about why the company did not act more quickly to tackle its wrongdoing.
"In the spring of 2014 ... I was told that there was a possible emissions non-compliance that could be remedied," Horn, president and CEO of Volkswagen Group of America, said in his statement published on a U.S. House of Representatives website.
"I was also informed that the company engineers would work with the agencies to resolve the issue," he said, without identifying the people providing him with the information.
It was not until this year, on Sept. 3, that Volkswagen told U.S. regulators it had installed so-called "defeat devices" in some diesel engines to mask their true level of toxic emissions. U.S. regulators made public the wrongdoing on Sept. 18.
Volkswagen has come under fire on both sides of the Atlantic for its handling of the crisis, with lawmakers, investors and customers saying it has been too slow to release information. Analysts are still unsure how widespread the cheating was.
Germany's Sueddeutsche Zeitung newspaper reported on Thursday that Volkswagen's manipulation software was switched on in Europe, citing a company spokesman.
The carmaker has previously said the software could be installed on up to 11 million vehicles, mostly in Europe, but that for the majority of them it "does not have any effect."
In a statement on Thursday, Volkswagen said it was still investigating whether or to what extent the software interfered illegally with vehicles.