The online activity by Frazier Glenn Cross follows a trend in which prolific posters on hate online forums are becoming "disproportionately responsible" for racist murders and mass killings, according to a report released on Thursday by the Southern Poverty Law Center, a non-profit civil rights organization.
The report said nearly 100 people in the last five years have been murdered by frequent users of one white supremacist website, Stormfront. The site describes itself as a community of "White Nationalists" and "the voice of the new, embattled White minority."
"It has been a magnet for the deadly and deranged," said Heidi Beirich, author of the report.
According to the report, past participants in forums on the website included Wade Michael Page, an Army veteran who opened fire at a Sikh temple in Wisconsin in 2012 killing six people before taking his own life.
Another was Anders Behring Breivik, a Norwegian extremist who massacred 77 people in a bombing and shooting spree in Oslo and at a nearby youth summer camp in 2011.
Stormfront owner Don Black told Reuters that Cross had never been allowed to post on his site, and that Breivik and other killers named by the SPLC had been banned.
"We're obviously a big website, and any site is likely to have a few unstable people pass through. Facebook, Twitter, and particularly Craigslist have had their share," Black added in a statement he posted on his website.
"Like all good propaganda, it's a mix of truth, half-truth and outrageous lies," Black wrote of the SPLC.
Frazier Glenn Cross often posted on Stormfront until he was banned from the site in 2005 after testifying in a trial against white supremacists, said Mark Potok, a senior fellow with the Southern Poverty Law Center.
Law enforcement and human rights groups have identified Cross as a former senior member of the Ku Klux Klan and someone who has repeatedly expressed hatred for Jewish people.
Cross, who also goes by the name Glenn Miller, later switched to another white supremacist forum, Vanguard News Network, where the center tracked his postings over the last five years.
"These killers are really hiding in plain sight on these forums," Beirich said.
Vanguard did not immediately respond to an email to the website seeking comment.
Cross faces one count of capital murder in the fatal shooting of Reat Underwood, 14, and his grandfather, William Corporon, 69, outside a Jewish community center and a charge of first-degree murder in the death of 53-year-old Terri LaManno. Cross is being held on a $10 million bond.
Potok called on law enforcement, particularly the U.S. Department of Homeland Security, to increase its focus on racist online forums.