Software is heavily documented and it is very unlikely that engineers would have taken the risk of modifying the software without approval at a high level of management, Mr. Lange said in an interview. "It's completely unrealistic that a lonely engineer" would have been responsible for the cheating, said Mr. Lange, who is founder and chief executive of Faster IT, a technology consulting firm. Volkswagen has not explained who inside the company was responsible for creating one of the biggest corporate scandals of the last decade. But in a German court filing last month, the company said that members of its management board "had no knowledge of the rule violation." The engine control software and onboard computer were provided by Bosch, one of the largest suppliers of electronic components for the auto industry. Bosch has been named along with Volkswagen as a defendant in class-action lawsuits filed by owners of Volkswagen-brand cars.