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(CNN) – The Southern Poverty Law Center monitors hate groups, and the man with a history of spouting anti-Semitic rhetoric that went on a shooting rampage Sunday had been on its radar since the early 1970s.
"He's a hardcore anti-Semite and white supremacist. And basically his life's work has been hating Jews," says Heidi Beirich, project director with the law center.
Frazier Glenn Cross is the suspect. He is accused of shooting to death a boy and his grandfather outside a Jewish community center and a woman at a nearby Jewish assisted living facility.
After he was apprehended at a nearby elementary school, Cross sat in the back of a patrol car and shouted "Heil Hitler!" Investigators have determined that the shootings could be a hate crime, Overland Park Police Chief John Douglass said at a Monday news conference.
But had he yelled "Allahu Akbar" instead, he could have also faced terrorism charges.
"This incident would be described as domestic terrorism if it had been Islamic extremism, and we need to take these kinds of threats much more seriously, because this really is terrorism," Beirich in an interview with CNN's "The Lead with Jake Tapper."
Cross spent his entire life "trying to destroy minorities and Jews. This was a political attack, just like an al Qaeda attack would be," she says.
"When we looked at domestic terrorism in the United States over the last several years, most of the threat here is coming from white supremacists like Cross, or from people who really hate the government," Beirich said.
The Southern Poverty Law Center sounded the alarm on Cross for decades, but Beirich says there is simply a lack of emphasis on these kinds of threats.
"We've been very critical of the Department of Homeland Security's intelligence efforts ... on this front, and more needs to be done," said Beirich.
"These domestic terrorists are hiding in plain sights on these forums. He's been producing rants almost
non-stop for a decade on a site with 12,000 posts. And we should probably be spending more attention to people on these forums for the potential of violence, like what happened yesterday," she says.