DENVER -- U.S. Marshals, along with FBI agents and members of the Safe Streets Task Force, are searching for a notorious "spam king" who walked away from a federal prison camp over the weekend.

Edward "Eddie" Davidson, 35, was serving 21 months in the minimum security facility in Florence, Colo., for sending hundreds of thousands of spam e-mails. He had pleaded guilty to tax evasion and falsifying e-mail headers.

He escaped on Sunday and was last seen in Lakewood, said Jeffrey Dorschner, with the Justice Department.

Federal prison camps have dormitory housing, a low staff-to-inmate ratio, and are work and program-oriented. Inmates in federal prison camps usually work at an adjacent prison, prison officials said. Dorschner did not say whether Davidson was working when he walked away.

As part of his sentence, Davidson had to pay $714,139 in restitution to the IRS and forfeit property he bought with the money he earned. Coincidentally, on Tuesday the IRS is selling the gold coins it had seized from him.

According to the stipulated facts contained in a plea agreement, Davidson's operation used false e-mail headers to disguise the sender. Prosecutors say some of the spam was meant to dupe stock investors and manipulate markets. Authorities say Davidson made at least $3.5 million sending e-mails for nearly 20 companies.

His business, Power Promoters, operated from July 2002 through April 2007. The primary nature of Davidson's business was to promote companies by sending spam, the U.S. Attorney's office said. During 2002 through the middle of 2005, Davidson's spamming activities were provided on behalf of companies to promote watches, perfume, and other items, authorities said.

But in the middle of 2005 through 2006, Davidson sent spam on behalf of a Texas company for purposes of promoting the sale of the company's stock. The company generated its income through selling stock (commonly referred to as "penny stock") on behalf of small companies on the public market.

Davidson, aided by several sub-spammers, sent hundreds of thousands of unsolicited e-mail messages to potential purchasers throughout the United States and the world, with messages touting the penny stock as an excellent investment. He operated his spamming activities from his home in Bennett, Colo., where he had a large network of computers and servers, which facilitated his business, the indictment said.