Volkswagen believes that only a small number of employees were behind the emissions scandal.
But its board chairman said on Thursday the company is still investigating and suggested the probe will 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.
Poetsch would not say if more staff might be suspended, but indicated the company's probe would be broad: "This is not only about direct but overall responsibility."
He said the investigation has so far analysed data from laptops, phones and other devices from 400 employees. More than 2000 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."
To avoid a repeat, Volkswagen will start road testing its vehicles with third-party emissions verifications, as lab tests - so far the norm in the US and Europe - had proved too easy to cheat.
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