The rigour of the Dow Jones Sustainability Index assessment criteria experienced something of a shock when on 21 September 2015, Volkswagen AG (VW) was listed as the industry group leader for Automobiles and Components. On 29 September 2015, the S&P Dow Jones Indices announced that VW was to be removed from the Dow Jones Sustainability Indices. It was because of the result of revelations that it had manipulated emissions tests to conceal the level of toxic pollutants issuing from its diesel engines in popular saloon cars in the United States. German prosecutors announced in June 2016 that they had opened an investigation into VW's former chief executive Martin Winterkorn over alleged market manipulation for not announcing earlier that the company had manipulated emissions tests. Shares in VW, which owns Audi and Porsche, dropped sharply from where they were when the emissions test cheating emerged in September 2015. Matthias Muller, who replaced Martin Winterkorn, apologized to shareholders for the scandal.