WOLFSBURG, Germany

A small group of Volkswagen engineers began working as early as 2005 on emissions cheating software after they were unable to find a technical solution to U.S. emissions controls as the automaker pushed into the North American market, executives said Thursday.

And when a technical solution was reached, it wasn’t used.

The company in September admitted to have cheated on U.S. diesel emissions tests with the help of software installed in engines. The software was built into 11 million cars globally, about 500,000 of which were sold in the United States between 2009 and 2015.

It has so far confirmed to have cheated only on the U.S. tests for the polluting emission nitrogen oxide. The U.S. tests are more rigorous than those in Europe.

In an update on the company’s investigation in the case, chairman Hans Dieter Poetsch said engineers in 2005 were unable to find a technical solution to U.S. nitrogen oxide emissions within their “time frame and budget” and came up with the software that manipulated results when lab testing was done.

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The failure of the company to employ a technical solution when it became available was a key issue, Poetsch said. “We are not talking about a one-off mistake, but a whole chain of mistakes that was not interrupted at any point along the time line,” he told reporters at Volkswagen headquarters in Wolfsburg.

He said Volkswagen was “relentlessly searching for those responsible” and that those who were would be brought to account.

“We still do not know whether the people who were involved in this issue from 2005 to the present day were fully aware of the risks they were taking and of the potential damage they could expose the company to, but that’s another issue we will find out,” he said.

CEO Matthias Mueller said the investigation so far had revealed that “information was not shared, it stayed within a small circle of people who were engineers.”

Poetsch confirmed the company had suspended nine managers for possible involvement in the scandal. He said there are so far no indications that board members were directly involved, but the company’s probe is ongoing and broad.