The recent killings of a U.S. Holocaust Memorial Museum guard and a Kansas abortion doctor came a few months after the Federal Bureau of Investigation stepped up efforts to pre-empt violence committed by just such political extremists working alone.

Associated Press

James von Brunn

Lone-wolf offenders continue to be of great concern to law enforcement," the agency said in a February memo reviewed by The Wall Street Journal. The FBI is "trying to identify a potential lone wolf before he or she would act out violently," Michael Ward, the bureau's deputy assistant director for counterterrorism, said in an interview earlier this year.

The lone-wolf initiative is one element of a broader strategy to fight domestic terrorism, dubbed "Operation Vigilant Eagle," launched late last year in response to what the memo identified as "an increase in recruitment, threatening communications, and weapons procurement by white supremacy extremist and militia/sovereign citizen extremist groups."

Vigilant Eagle's creation was first reported by the Journal in April.

The memo, and the recent killings, also show the limits of the lone-wolf effort. Both James von Brunn, who is charged with the Holocaust Museum shooting, and Scott Roeder, the man arrested in the murder of George Tiller in Kansas, had openly expressed to associates and on Web sites their extremist views, on anti-Semitism in Mr. von Brunn's case and on abortion in the case of Mr. Roeder. The FBI, in fact, was aware of Mr. von Brunn because of the postings but wasn't tracking him.

Neither man appears to have been active in groups that might have tipped off authorities to the danger. In the search for potentially violent individual extremists, "an emphasis should be placed on the identification of individuals who have been ostracized from a group for their radical beliefs," the FBI memo said. It added that officials should look for "those who have voluntarily left a group due to their perception of the group's inactivity, or those forced from the group for being too extreme and or violent." That description doesn't appear to have fit either Mr. von Brunn or Mr. Roeder.

"The lone wolf is arguably one of the biggest challenges to American law enforcement," said Mike Rolince a former FBI counterterrorism official who spent years focused on domestic extremists. "How do you get into the mind of a terrorist? The FBI does not have the capability to know when a person gets up in middle America and decides: 'I'm taking my protest poster to Washington or I'm taking my gun.' "

While much of the focus in recent years has been on international terrorism and on militant groups, authorities say the lone-wolf syndrome has always been a major concern, borne out by high-profile incidents such as the 1995 Oklahoma City bombing, the 1996 Olympic bombing in Atlanta and the series of bombings carried out over nearly two decades by Theodore Kaczynski, who lived in a remote cabin in Montana.

The stepped-up attention to the issue in recent months is part of a broader worry about rising threats and violence from political extremists. There are no concrete data showing recent trends. The FBI's hate-crime reports are more than a year behind. Still, the most recent data showed that from 2005 to 2007, the number of such incidents rose more than 6%.

In addition to the recent killings in Washington, D.C., and Kansas, recent lone-wolf cases include the killing of a soldier in Little Rock, Ark., last month, allegedly by a converted Muslim extremist, Abdulhakim Muhammad. Last August, a Florida man attending bail-bondsman training was arrested for making threats against then-Sen. Barack Obama and President George W. Bush. And in October, two men who identified themselves as skinheads were arrested in Tennessee where they were plotting to go on a nationwide killing spree targeting African-Americans.

The FBI memo also noted the scant academic study to date of violent individual extremists, and said the agency had recently stepped up efforts to analyze their actions. A study launched in partnership with Harvard University, the memo said, would seek to define characteristics and behavior that signal a potential lone-wolf offender.

Harvard spokesman who contacted various departments to ask about the study said he was unaware of it. The FBI said there was no date for completion.

The FBI memo also called on bureau offices around the country to assess whether the leaders of known extremist groups might be open to cooperating with law enforcement in identifying potential lone offenders. The FBU advised its offices not to initiate contact at this time.

Meantime, the bureau has been working with the U.S. military and with prison authorities to identify people who may raise concerns, hoping that "anyone who would be inclined to act out, we'd have a sporting chance to take any kind of preventative measures we can," Mr. Ward said.

One constraint facing authorities is the need to balance monitoring of potential violent extremists with the protection of a suspect's civil liberties. The memo noted that the study had been cleared by the FBI's "institutional review board, which reviews all FBI research involving human subjects in order to help protect the rights and welfare of those subjects."

"Their hands are tied a little bit," said Heidi Beirich, of the Southern Poverty Law Center, which monitors hate groups. "We have to protect freedom of speech. It's kind of complicated."

Write to Gary Fields at gary.fields@wsj.com and Evan Perez at evan.perez@wsj.com

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