BERLIN (AP) — German prosecutors say that automaker Volkswagen as a whole is responsible for the 2015 diesel emissions cheating scandal, a day after the company said it would accept a one-billion euro fine (1.18 billion dollars).

Braunschweig senior prosecutor Klaus Ziehe said Thursday his investigation concluded the company failed to properly oversee its engine development department, but that the scandal cannot be attributed to a single department alone.

More than 10 million diesel vehicles were sold internationally with illegal emissions-controlling software.

Ziehe said the fine was "painful," adding it's the highest amount of money to be ever fined against a German company.

Prosecutors say the fine has to be paid within six weeks.

The scandal has already cost Volkswagen $20 billion in fines and civil settlements in the U.S.