As much as law enforcement would have loved to have been lying in wait outside the Holocaust museum for James von Brunn, there are limits to how much they could have anticipated that attack, says National Public Radio. That’s because that shooting – which left a security officer dead – and others appear to have been the work of what the FBI calls “lone wolves.” Lone wolves are killers who come out of nowhere – with no links to terrorist and extremist groups – to attack alone. “If a person makes a decision – ‘I am going to do it on my own, I will tell no one, and I will leave no telltale psychological fingerprints anywhere around’ – that is very hard  to stop,” says Clint van Zandt, a former FBI behaviorialist.
Most lone wolves fall into four categories: religious extremists, political terrorists, people who have long-standing mental problems, and those who just snap. Sam Rascoff, a former police intelligence officer now at the New York University School of Law, says, “As a practical matter, [law enforcement] can’t possibly play man-to-man defense against absolutely everyone who some day might translate some sort of hateful ideology into violent action.” Last year the FBI launched Operation Vigilant Eagle to reach out to white supremacists and militia groups and convince them to report outliers to the authorities.