A federal jury in Roanoke has convicted an Arizona man of illegally selling nitrous oxide as a drug over the Internet almost one year after a Virginia Tech student from Fairfax died after inhaling the gas.

Prosecutors hailed Thursday's verdict in U.S. District Court as the first of its kind, dealing what they hope is a heavy blow to Internet and mail-order companies that sell the gas to clients who want to inhale it for a short and intense high.

Because of nitrous oxide's legitimate uses, prosecutors have had trouble proving that the sale of the legal but potentially deadly gas was akin to selling any other drug across state lines. Nitrous oxide cartridges are commonly sold to make whipped cream, and nitrous gas is often mixed with oxygen for use as a sedative in dentists' offices. The cartridges can be found all across the country in head shops, gourmet food stores and convenience stores.

Andrew McCoy, 20, died last November after inhaling the gas in his apartment in Blacksburg. Authorities found a number of used cartridges near his body, along with a box linking them to a Tempe, Ariz., company. Police traced the cartridges to the now-defunct Web site, www.bongmart.com, where McCoy had purchased them days before.

The operator of bongmart.com, Lawrence Teiman, 36, was found guilty of five felony counts of violating the federal Food and Drug Act, specifically for selling a misbranded drug over state lines while trying to mislead law enforcement officials. According to prosecutors, Teiman sold boxes of the three-ounce cartridges on his site, marketing the product as a drug, but covering his tracks by saying it was for "food use only."

Teiman could face up to 15 years in prison and a fine of $1.25 million when he is sentenced in January.

"The biggest concern for us is that nitrous oxide use certainly is a fast-growing problem," said Assistant U.S. Attorney Craig "Jake" Jacobsen, who prosecuted the case. "Everyone has considered it a free pass because people think that it's harmless, and they have been selling it with impunity. Unfortunately, it took a death to bring it to our attention."

Jacobsen said much of the difficulty with bringing such a case is that it isn't illegal to sell nitrous oxide. Instead, prosecutors have to prove that the sale is intended for misuse and that the seller knows clients will use the gas as a drug. Teiman's attorneys argued that he simply sold a legal product and labeled it for its proper use.

McCoy, a computer sciences major and Eagle Scout who graduated from Thomas Jefferson High School in 1998, told friends that he researched nitrous oxide on the Internet and had decided it was a safe alternative to other drugs and alcohol, his mother said yesterday. McCoy, who had twice bought cartridges over the Internet, asphyxiated Nov. 14 after he tied a plastic bag over his head to inhale the gas.

"Terrible consequences to pay for believing what he read on the Internet," said McCoy's mother, Suzanne, who also said the family plans to scatter his ashes on Skyline Drive today. "I am absolutely thrilled that the government took this so seriously because it would have been easy for the police to say that this was some dumb college kid who killed himself with drugs. People need to know it's a dangerous drug."