However, none of its top bosses could have known of the full extent of the scandal until it broke in September of that year, the company claimed in a statement late Wednesday.
VW, a former paragon of German industry with ambitions to become the world's biggest carmaker, has been plunged into its deepest-ever crisis by revelations that it installed emissions-cheating software into 11 million diesel engines worldwide.
In a bid to identify the masterminds behind the engine-rigging that has sent shockwaves through the automobile sector all around the world, the embattled German giant is conducting an internal investigation, the preliminary results of which are to be published next month.
It was the ICCT that alerted VW's cheating practices to the US environmental agency, the California Air Resources Board (CARB), which then went public with the accusations last September.
"This memo was included in his extensive weekend mail. Whether and to which extent Mr. Winterkorn took notice of this memo at that time is not documented," the statement said.
"According to current knowledge, the diesel matter, as it was treated as one of many product issues facing the company, did not initially receive particular attention at the management levels of Volkswagen."
On top of still unquantifiable regulatory fines in a range of countries, VW is facing a slew of legal suits, notably in the US and Germany, from angry car owners, as well as from shareholders seeking damages for the massive loss in the value of their shares since September.
