Criminal defense lawyers say they will ask the U.S. Supreme Court to review a novel legal approach the government has begun using to win stiff mandatory prison terms for those who've downloaded child pornography from file-sharing sites.

At issue is a new interpretation of a 1986 law, amended in 2003 under the Protect Act, intended to curb child-porn advertising by imposing a mandatory 15-year prison term on anyone convicted of publishing "notice" offering to distribute kid porn across state lines.

Last year, Walter Sewell, a 43-year-old pharmacist from Missouri, was sentenced under the act to the automatic 15-year prison stretch after downloading and sharing sexually explicit images over the Kazaa file-sharing network. He was the nation's first defendant to be prosecuted under what authorities admit is an "innovative use" of the Protect Act.

"He's getting more time than people actually molesting kids," says Eric Chase, a California attorney representing Sewell. "He didn't make it. He didn't sell it. He didn't even buy it."

Last year a jury found that Sewell downloaded thousands of images of child pornography using Kazaa and made them available to others from his share folder. Chase conceded that his client is guilty of distributing child pornography, which normally carries a five-year sentence.

But he argues that sharing such files over Kazaa shouldn't qualify as advertising under the law, and therefore shouldn't be subject to the mandatory 15 years.

Last week, the 8th U.S. Circuit Court of Appeals disagreed and upheld Sewell's sentence and conviction (.pdf). On Thursday, Chase said he would ask the Supreme Court to review the case.

In its ruling, the 8th Circuit found that the "descriptive fields" identifying the files in Sewell's share folder alerted Kazaa users that he was offering such illegal material. The files were named "Pedo 12-14yr.jpg," "PBC Bro's given it to Mom&Sis" and "Underage Pornography Erotica," among others.

"It's an innovative use of the statute," said Don Ledford, a spokesman for prosecutors in the Western District of Missouri, in Kansas City. "We were the first district in the country to use the statute that way to get the 15-year mandatory minimum."

U.S. attorneys throughout the country, he said, are beginning to experiment with charging Kazaa child pornography users like Sewell. Kazaa is an open system, meaning the authorities can easily learn a user's identity from his internet protocol address by subpoenaing the internet service provider. In Sewell's case, the FBI made the case.

"Prior to the internet playing such a dominant role among pedophiles and child sexual exploiters, publishing a notice for child pornography might have meant classified advertising or a notice online in a chat room or message board offering to sell child pornography," Ledford continued. "What's innovative here is the Kazaa software itself generates that notice."

In 1986, Congress approved the statute under which Sewell was prosecuted, and it originally carried a mandatory 10-year minimum sentence. The sentence was increased in 2003 to 15 years without the possibility of parole.

The law was adopted to counter illegal smut advertising in the traditional sense. Still, even three decades ago, Congress was concerned about preventing the exchange of pornographic materials through computers.

Although Kazaa did not exist in 1986, Congress specifically mentioned one of its technological forebears, computer "bulletin boards," as being a source of an illicit child-porn trade.

In upholding the conviction, the 8th Circuit ruled Jan. 17 that "Kazaa's purpose is to allow users to download each other's files, and the purpose of the descriptive fields is to alert interested users to the content of downloadable files."

The court reiterated language from a 10th U.S. Circuit Court of Appeals decision last year, a decision often cited by the Recording Industry Association of America in its music downloading lawsuits against Kazaa file sharers.

"A Kazaa file's descriptive fields are like a roadside sign to a self-serve gas station at which the owner need not be present to distribute fuel to passing motorists," the court wrote. "No one would stop at the station without the sign telling them where the gas station is. The context of such a sign tells motorists that the owner of the station is offering to distribute fuel to them."