Volkswagen America CEO Michael Horn has played the "rogue employee" card to explain how and why his cars' engine software cheated in pollution tests.

While being grilled by the US House Committee on Energy and Commerce on Thursday, Horn said he only learned of the existence of the so-called emissions-hoodwinking "defeat device" in September of this year, when regulators uncovered the nefarious software.

Horn, like the rest of VW's upper crust, claims that management was entirely in the dark about the fact that more than half a million cars in the US had been rigged to suppress emissions while being tested, only to surpass the EPA-allowed levels of pollutants by more than 30 times when driven on the open road.

"This was not a corporate decision from my point of view," Horn said while under oath.

"To my knowledge this was a couple of software engineers."

You can read Horn's written testimony to the committee here [PDF].

Despite being sure that the defeat devices were the work of a close-knit cabal with no communication to management, Horn said VW has not yet determined who those couple of engineers were and the investigation remains ongoing.

Congress, however, was not exactly buying Horn's investigation, and more than one member suggested VW knew a lot more about the emissions workaround than they've let on.

"We'll hear that the use of defeat devices are incompatible with Volkswagen's corporate culture," said Rep. Jan Schakowsky (D-Il). "And I want to tell you Mr Horn, I don't buy it."

Rep. Chris Collins (R-NY), himself a former engineer, noted that if this defeat device was the work of two Volkswagen engineers acting alone, the company's intellectual property department would have every reason to seek to patent the innovation unless they were directed otherwise by management.

"You're telling me these engineers snuck that code into the software and no one said this is breakthrough technology, we need to patent this," said an incredulous Collins.

"Either your entire organization is incompetent when it comes to intellectual property, and I don't buy that, or they are complicit at the highest levels in a massive cover-up that continues today." ®