U.S. marshals along with FBI agents searched Wednesday for spam king Edward "Eddie" Davidson, 35, who was serving a 21-month sentence for tax evasion and falsifying e-mail headers, KMGH-TV, Denver, reports.

Authorities said Davidson made at least $3.5 million sending e-mails for various companies from his home.

Davidson was assigned to a minimum-security prison camp in Florence where inmates are housed in dormitories and the ratio of staff to prisoners is low, said Jeffrey Dorschner of the Justice Department.

Dorschner did not say whether Davidson was working when he walked away on Sunday.

He was last seen in a suburb of Denver.