by Senior National Security Producer Suzanne Kelly
The arrest this week of four Georgia men charged with plotting to attack government officials with explosives and a biotoxin raises the question of just how big of a threat are homegrown terrorists in the United States?
While security experts obviously can't put a ranking on a would-be terrorist, there are some reasons why the homegrown variety pose a unique challenge to law enforcement.
"Homegrown terror groups tend to be small and tight-knit, which makes detection and infiltration a law enforcement challenge," said CNN National Security Analyst Fran Townsend. "These groups vary widely as to their grievance and motivation, but all use violent means to get attention."
The most deadly domestic terror attack in the United States remains the bombing of the federal building in Oklahoma City in April of 1995. Timothy McVeigh, who headed a small group of individuals, planted the truck bomb that killed 168 people.
Dr. Anthony Lemieux, a visiting professor at Emory University in Atlanta and an investigator with the National Center for the Study of Terrorism and Responses to Terrorism (START), says there are plenty of cases of homegrown terror within the United States.
"It's interesting because on the one hand, you've got relatively small clusters, but for instance - Timothy McVeigh was one guy with a couple of assists and caused massive damage, so with the right kind of explosives, a team of four people can be quite lethal and quite dangerous," said Lemieux.
And that's part of what makes homegrown terrorists so difficult for law enforcement to detect. Though there are, according to Lemieux, common grievances that bring these individuals together.
Lemieux and his colleagues have researched terrorist motivations, and found that many grievances shared among particular groups within the United States tend to be anti-government, anti-tax or some may share white supremacist views. They also typically share common targets.
"They will go after civilians particularly, or people related to the justice system," said Lemieux.
Another unique problem in investigating these would-be terrorists, according to experts like Lemieux and Townsend, is that having extreme views and sharing them isn't against the law - making it difficult for law enforcement to infiltrate smaller groups and determine whether they are just disgruntled, or an actual threat.