A top Volkswagen AG official on Tuesday defended the German automaker’s reform efforts in the aftermath of the emissions cheating scandal, a month after the company’s independent compliance monitor faulted executives for not pushing harder to recast the corporate culture.

Hiltrud Werner, Volkswagen’s head of integrity and legal affairs, said the company has been troubled and puzzled by how long the emissions fraud carried on before coming to light. Speaking at a conference in Washington, Werner, formerly Volkswagen’s chief auditor, said the company is ”already making extremely good progress” at developing a speak-up culture.