WOLFSBURG, Germany — The chairman of Volkswagen said on Thursday that the decision by employees to cheat on emissions tests was made more than a decade ago, after they realized they could not meet United States clean air standards legally.

Hans-Dieter Pötsch, the chairman of Volkswagen’s supervisory board, said the cheating took place in a climate of lax ethical standards.

“There was a tolerance for breaking the rules,” Mr. Pötsch said here on Thursday during his first lengthy news conference since the company admitted in September that 11 million cars with diesel engines were rigged to fool emissions tests. The fallout from that decision has confronted Volkswagen with “the biggest test” in its history, Mr. Pötsch said.

Mr. Pötsch and Matthias Müller, the chief executive of Volkswagen, presented the results so far of an internal inquiry that is still underway. Although the company is not ready to identify culprits, the preliminary findings confirmed widespread suspicion that the scandal occurred because the company’s ambitions in the United States collided with air quality rules that were, and still are, more stringent than Europe’s.