From ABC via Yahoo

Federal authorities have issued a warning there could be “acts of violence” in the homeland sparked by the recent massacre of 16 civilians in Afghanistan allegedly by an American soldier.

“The FBI and DHS [Department of Homeland Security] are concerned that this event could contribute to the radicalization or mobilization of homegrown violent extremists [HVEs] in the homeland, particularly against U.S.-based military targets which HVEs have historically considered legitimate targets for retaliation in response to past alleged U.S. military actions against civilians overseas,” the FBI and DHS said in a joint “awareness bulletin” to law enforcement agencies Wednesday. More from Yahoo

Except from: Hearing before the House Committee on Homeland Security
”Understanding the Homeland Threat Landscape – Considerations for the 112th Congress”
February 9, 2011

Homegrown Extremist Activity Remains Elevated
In addition to threats emanating from outside the country, we also remain concerned that homegrown violent extremists (HVEs) continue to pose an elevated threat to the Homeland. Plots disrupted in Washington, D.C., Oregon, Alaska, and Maryland during the past year were unrelated operationally, but indicate that the ideology espoused by al-Qa’ida and its adherents is motivating, or being used as a justification by, individuals to attack the Homeland. Key to this trend has been the development of a US-specific narrative, particularly in terrorist media
available on the Internet that motivates individuals to violence. This narrative—a blend of al-Qa‘ida inspiration, perceived victimization, and glorification of past Homegrown plotting—addresses the unique concerns of like-minded, US-based individuals. HVEs continue to act independently and have yet to demonstrate the capability to conduct sophisticated attacks, but as Fort Hood shooter Nidal Hasan demonstrated, attacks need not be sophisticated to be deadly.

• Similar to 2009, arrests of HVEs in the United States in 2010 remained at elevated levels, with four plots disrupted in the Homeland. The individuals involved were motivated to carry out violence on the basis of a variety of personal rationales, underscoring the continued intent by some HVEs to take part in violence despite having no operational connections to terrorists overseas.
• Increasingly sophisticated English-language propaganda that provides extremists with guidance to carry out Homeland attacks remains easily accessible via the Internet. English-language web forums also foster a sense of community and further indoctrinate new recruits, both of which can lead to increased levels of violent activity.
• The prominent profiles of US citizens within overseas terrorist groups—such as Omar Hammami in al-Shabaab and Anwar al-Aulaqi in AQAP—may also provide young U.S.-based individuals with American role models in groups that in the past may have appeared foreign and inaccessible. These individuals have also provided encouragement for homegrown extremists to travel overseas and join terrorist organizations.