Hiroshi Nakamura heard the news early Saturday morning last month from a U.S. colleague: Volkswagen AG had just admitted to years of cheating on emissions tests.

Nakamura wasn't sure, but he had a hunch that his employer, Horiba Ltd., an obscure Japanese manufacturer that makes about 70 percent of the world's auto emissions testing systems, had played a key role in breakrng a scandal involving one of the giants of the industry. Volkswagen, whose stock has lost more than one-third of its value since the news broke Sept. 18, out- employs Horiba by almost 100-to-1.

Turned out Nakamura, the 42-year-old chief manager of automotive strategy at Horiba, was spot on. U.S. researchers had relied on Horiba's portable emissions measuring systems in a multiyear round of testing that ended up catching Volkswagen in a lie about engines it had billed as "clean" diesels. Horiba's equipment helped tip off the researchers to a scheme in which 11 million Volkswagen group cars around the world pollute more on the road than in lab tests, exceeding U.S. limits by as much as 40 times more than the law allows.