WOLFSBURG: Volkswagen believes that only a small number of employees were behind the emissions scandal, but its board chairman said Thursday the company is still investigating and suggested the probe does not exclude top managers.

In an update on the German automaker's attempt to get to the bottom of the scandal, Hans Dieter Poetsch said "we are relentlessly searching for those responsible for what happened and you may rest assured we will bring these persons to account."

He confirmed the company had suspended nine managers for possible involvement in the scandal, in which the company was found to have cheated on US diesel emissions tests with the help of software installed in engines. The software was installed on 11 million cars globally, about 500,000 of which in the US.

Poetsch said there are so far no indications that board members were directly involved, but said the company's probe would be broad: "This is not only about direct but overall responsibility."

He said the investigation has so far analyzed data from laptops, phones and other devices from 400 employees. More than 2,000 have been informed in writing that they cannot delete any data in case it becomes relevant to the investigation, he said.

External auditors have already gone through 102 terabytes of data, which he said was the equivalent of 50 million books.

"I'm not saying all of those people are under suspicion, but what it means is that on computers, sim cards, or USB sticks there might be information that could be important," he said.

"We still believe that only a comparatively small number of employees was actually actively involved in the manipulations."

CEO Matthias Mueller said that the scandal had so far not caused the "massive slump that some feared earlier." He said "the situation is not dramatic, but as expected it is tense." Sales in the U. fell nearly 25 percent in November, the first month to show the full impact of the scandal. Figures for the European Union are due next week.

"We are fighting for every customer and every car."

He suggested that the company was not considering any cuts to fulltime jobs, but that it might have to shed some temporary workers.

"Temporary jobs are a tool of ensuring flexibility, that is not new," he said. "If changes come to our production, then this may have an impact on the number of temporary workers."

Mueller said Volkswagen's finances are strong enough, however, that the company does not have to consider selling any units to cope with the costs of the scandal as has been speculated by some. The automaker has estimated the scandal would cost 6.7 billion euros, though analysts expect that figure to ultimately be much higher.

To help restore confidence in the company and "prevent something like this from ever happening again," Poetsch announced that Volkswagen was instituting new, more stringent and transparent emissions testing for all of its vehicles. He said Volkswagen would go beyond lab tests — so far the norm in the US and Europe — had proved too easy to cheat.

"Our emissions tests will, in future, be verified by external and independent third parties," he said. "We will also be introducing universal on-road emissions measurements during real-life driving, and we hope that will help us win back trust."