Under intense questioning from politicians from both sides of politics and under oath, Horn told the House of Representatives oversight and investigations committee on energy and commerce that "to my understanding, this was not a corporate decision, this was something individuals did".
"This was a couple of software engineers who put this in for whatever reason," Horn claimed.
When pressed further about the believability of his claims, the Volkswagen executive admitted, "I agree it's very hard to believe, and I personally find it hard to believe".
Asked why these engineers decided to cheat, Horn speculated that might be "pressure in the system to get resolutions" and the company's strong cost focus.
During his scripted opening remarks, Horn told the panel members that "in the spring of 2014 when the West Virginia University study was published, I was told that there was a possible emissions non-compliance that could be remedied".
Horn continued: "I was also informed that the company engineers would work with the agencies to resolve the issue. Later in 2014, I was informed that the technical teams had a specific plan for remedies to bring the vehicles into compliance and that they were engaged with the agencies about the process."
Around three weeks ago Volkswagen admitted to the US Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) that it had installed algorithms to help it illegally pass emissions tests. Horn said, during questioning, that he only learnt of the defeat devices a few days before public disclosure.
The company has confessed that up to 11 million vehicles sold worldwide with the EA189 diesel engine have code in them that's designed to help it fraudulently pass emissions testing. Around 482,000 of these cars were sold in the United States.
A Volkswagen spokeswoman later told Automotive News that Stateside three different generations of the EA189 were used. The first generation engine, of which 325,000 were sold in the US, are claimed to be the most difficult to fix.
Second generation engines number around 90,000 in the US and will have fixes ready by around the middle of 2016. Third generation motors, of which there roughly 67,000 in the States, can be made compliant via a software change alone as they already meet emissions standards.
The earlier engines are believed to require both hardware and software changes.