WASHINGTON – Volkswagen’s top U.S. executive offered deep apologies yet sought to distance himself Thursday from the emissions scandal enveloping the world’s largest automaker, asserting top corporate officials had no knowledge of the cheating software installed in 11 million diesel cars.

Though he said he hadn’t been briefed on the preliminary findings of the ongoing internal investigation, Volkswagen of America CEO Michael Horn told a congressional subcommittee that a tiny group of software developers in Germany was responsible for the computer code that enabled the cars to trick U.S. government emissions tests. Three lower-level managers have been suspended.

“To my understanding this was not a corporate decision, this was something individuals did,” Horn said, adding that he felt personally deceived.

That explanation left members of the House panel investigating the scheme incredulous.

“I agree it’s very hard to believe,” Horn conceded.

Rep. Chris Collins, R-N.Y., was among the lawmakers who said he couldn’t accept VW’s characterization that “this was the work of a couple of rogue engineers.” Collins, an engineer, suggested that such a far-reaching cheating strategy couldn’t be pulled off without the complicity of high-ranking supervisors across several parts of the company.

“What I’ve picked up here and I hope you can relay back to your board, the folks running Volkswagen back in Germany, is that the response so far is inadequate,” Collins said. “It’s a sign of arrogance. It’s a sign of not admitting yet the severity of your problem.”