Volkswagen started the week promoting a bold plan for its electric-car future. As the week ended, the German carmaker was grappling again with a potentially huge obstacle to achieving that transformation: the lingering stench from its diesel-car past.

In a lawsuit filed late Thursday accusing Volkswagen of defrauding American investors, the Securities and Exchange Commission said the carmaker’s former chief executive, Martin Winterkorn, knew about a “massive” emissions fraud in November 2007.

If proven, that would be almost at the scheme’s inception, much sooner than Mr. Winterkorn or Volkswagen have previously admitted and nearly seven years earlier than federal prosecutors alleged in a criminal indictment filed against him and several other Volkswagen executives last year.

The commission’s timeline severely undercuts Volkswagen’s position that the plot to deceive American regulators about the exhaust levels of the company’s diesel vehicles was entirely the work of lower-level employees and that Mr. Winterkorn and other top managers only learned of it shortly before the Environmental Protection Agency publicly accused Volkswagen of carrying it out in September 2015.