So far, authorities believe James von Brunn, the Maryland man accused of killing a security guard at the U.S. Holocaust Memorial Museum in Washington, acted alone.
But the anti-Semitic and racist views he has expressed in decades of rants - in court testimony, on his Web site and in a self-published book - represent the convictions of a deeply rooted community of extremists now taking advantage of technology to attract new recruits.
At least 13 such outfits now operate in Maryland, according to trackers of hate groups. They range from bands of racist skinheads to organized committees of white nationalists that advertise and sponsor well-attended conferences in hotel ballrooms.
Nationwide, the number of hate groups climbed from 602 in 2000 to 929 in 2008, according to the Southern Poverty Law Center - an expansion fueled by anger against immigrants and, more recently, the election of the nation's first black president.
A report released Tuesday by the Leadership Conference on Civil Rights Education Fund said white supremacist activity online spiked after President Barack Obama's victory.
The Leadership Conference's report came the same day Attorney General Eric H. Holder Jr. urged Congress to pass tougher hate-crime laws. The killing of Holocaust Museum security guard Stephen T. Johns last week and the recent slaying of a doctor who performed late-term abortions in Kansas serve as reminders of the "potential threat posed by violent extremists," Holder said.
But how to identify genuine threats among the constitutionally protected rants and boasts that proliferate in cyberspace remains a thorny question for law enforcement.
"We have to have information that a crime has been committed or is in the planning stages of being committed in order to act," said Bret Kirby, who supervises domestic terrorism investigations for the FBI in Baltimore. "Anybody may consider what they are saying offensive, nevertheless, the First Amendment of the Constitution provides that we have free speech."
In Maryland, the number of hate crimes reported over the past decade has fluctuated between a low of 150 in 2007 and a high of 248 in 2003, according to the FBI.The Anti-Defamation League counted 22 incidents of anti-Semitism in 2008, up from 19 the year before. Of the 2008 events, 17 involved harassment and 10 involved damage to property.
