Bardazzi added that he believed the videos were changing popular sentiment about the war in Iraq the same way the images of fighting during the Vietnam War affected public opinion.
Today, nearly every active guerrilla group has an online presence, spread across hundreds of Web sites, according to Gabriel Weimann, who was until recently a fellow at the federally funded U.S. Institute of Peace.
Many of the sites are as slick as those of Fortune 500 corporations. One radical Islamic site displays pictures of President Bush and his main ally in the war, British Prime Minister Tony Blair, with stitches covering their bodies and promises that this scene will be "coming soon." It also urges boycotts of Coca-Cola Co., Nike Inc. and other U.S. corporations with an extensive presence overseas.
An Undetectable Hideout
With more than 1 billion linked computers, the Internet is an ideal hiding place for underground groups. The technology allows users to mask their identities and change them on a whim by throwing away old e-mail accounts and creating new ones.
Location can be hidden by hopping virtually from computer to computer. A message that appears to come from Australia, for instance, may actually come from someone who has accessed the Australian computer by going through the Netherlands via South Korea after originating in Jordan.
Secrecy is helped by the proliferation of free e-mail and Web hosting services that require users to give a minimal amount of information, which is rarely verified.
Terrorism investigators first began to see the name Abu Maysara in January in the Muntada Al-Ansar and Islah chat rooms, which are password-protected and only available to users who pass a background screening interview with a battery of questions including such things as whether they have ever attacked U.S. citizens and whether they have been imprisoned. Abu Maysara confirmed Zarqawi's presence in Iraq and took credit for several attacks on U.S. and other coalition troops.
Investigators believe it was the Ansar site that, in May, carried the first video depicting the beheading of Nicholas Berg, the young Pennsylvania businessman who was in the country looking to make money repairing radio towers.
For months, U.S. agents had been chasing the site, which was once based in Alexandria. By the time Berg was killed, the site had been moved to Malaysia.
Authorities managed to get it shut down again, but only temporarily. Ansar recently reappeared on a server in West Lafayette, Ind.
In June, the government's legal assaults suffered a setback when a computer programmer in Idaho was acquitted of a criminal charge that he had run a Web site that included edicts calling for violence. Deputy Defense Secretary Paul D. Wolfowitz has told Congress that the government will continue to pursue operators of such sites.
Feeling the pressure, Abu Maysara has been experimenting with new ways to get his message out effectively, investigators said. The problem with the Berg posting was that it was relatively easy for authorities to stop its distribution because it was only placed on one or two Web sites. E-mailing the video was out of the question because the file was too large.
Abu Maysara could not use the free Web hosting services from Yahoo or other companies because those services limited the number of people who can view a file.
But some time last month, Abu Maysara found a silver bullet -- a technology called YouSendIt.