The co-conspirators then engaged in deceptive and manipulative trading practices to boost the price and volume of the company's stock, the DOJ said. In some cases, members of the conspiracy encouraged investors to purchase companies' stock by giving the investors free-trading shares in return for buying blocks of shares at agreed-upon prices, thereby creating the illusion of trading volume and active investor interest.

In other instances, members of the conspiracy bought and sold shares of the companies' stock between and among themselves to give the appearance of investor interest, the DOJ said.

The co-conspirators also falsely manipulated the price and volume of each company's stock by making materially false and misleading statements in news releases and in spam e-mails distributed by Medlin and other spammers to tens of millions of U.S. e-mail addresses, in an effort to create artificial demand for the companies' stock, the DOJ said.

In related actions, the U.S. Securities and Exchange Commission has filed civil charges against Saquella and Kaplan for their part in the schemes to manipulate the price and volume of the companies' securities.

Three other defendants, Steven P. Luscko, Gregory A. Neu and Brian G. Brunette, have pleaded guilty and have been sentenced in federal court in Alexandria for their roles in related stock manipulation schemes. Luscko and Neu were each sentenced to five years in prison and Brunette was sentenced to one year in prison.