A California wine dealer was found guilty by a federal jury in Manhattan of selling counterfeit bottles to collectors after a federal trial that featured testimony from billionaire William Koch.

The merchant, Rudy Kurniawan, was convicted today of mail fraud and wire fraud. A prominent dealer of purportedly rare and expensive wine, Kurniawan was accused by the government of defrauding collectors and others about his business in multiple schemes from 2004 to 2012.

Koch, a wine collector who has mounted a legal campaign against counterfeiting in the industry, testified in the trial before U.S. District Judge Richard Berman that Kurniawan sold him phony vintages. Koch also sued Kurniawan in 2009 in California state court in Los Angeles.

Kurniawan, an Indonesian who was living in Arcadia, California, faces as long as 20 years in prison on each of the fraud counts, according to prosecutors. He’s scheduled to be sentenced April 24.

In April 2013, Koch won $12 million in punitive damages in a lawsuit against wine consignor Eric Greenberg over allegations that he made fraudulent representations about the authenticity of certain bottles that Koch had bought. Koch is the founder of West Palm Beach, Florida-based Oxbow Carbon & Minerals LLC.

The case is U.S. v. Kurniawan, 1:12-cr-00376, U.S. District Court, Southern District of New York (Manhattan).