Is inflammatory speech motivating American assassins?

Soon after Jared Loughner shot Rep. Gabrielle Giffords in the head on Saturday, an Arizona sheriff suggested that inflammatory speech was partly to blame. Sheriff Clarence Dupnik implied that Loughner was motivated by vitriolic speech from "people in the radio business and some people in the TV business." Dupnik’s remarks have set off heated debate - not least, of course, on right-wing talk shows. Rush Limbaugh said, for instance, that the sheriff had "made a fool of himself." Dupnik replied "[Limbaugh] attacks people, angers them against government, angers them against elected officials and that kind of behavior in my opinion is not without consequences." It is time, the sheriff said, for the country to "do a little soul searching" about the tenor of public speech. That's a contrarian opinion in America, where most inflammatory speech is not only lawful - it is "protected" by the First Amendment to the U.S. Constitution.

Debate and soul searching are worthwhile, but it would be more useful to search for data: to study cases like Loughner’s, to discover whether speech in fact contributed to violent threats and attacks like his. This would be an important contribution to the study of inflammatory speech, and unfortunately, the United States has produced a number of recent cases for such investigation.

Last March, for example, just after the U.S. Senate passed legislation to provide national health care, an enraged Charles Alan Wilson began phoning U.S. Sen. Patty Murray’s Seattle, Washington office, leaving terrifying voice mail messages such as, "You're dead fucking meat, Murray! You're dead fucking meat! Baby killer, Murray." Murray had voted for health care reform which, Wilson had apparently concluded, would raise the cost of his own medical care. “Kill the fucking senator! Kill the fucking senator! I'll donate the lead," he said in one recorded message. And in another: "I hope somebody kills you, and I hope somebody kills [Obama]. Yes, die, dead. You're signing my death warrant, so I want to sign yours, fucking bitch."

In October, Wilson was sentenced to a year and a day in prison; it is a crime to threaten a U.S. public official, in one of the few exceptions to the United States' uniquely broad law protecting speech. By the time he was sentenced, Wilson was reportedly ashamed of what he had done. A cousin of his told a Seattle newspaper that Wilson had been deeply influenced by the right-wing television personality Glenn Beck.

And just four months after Wilson began threatening to kill Senator Murray, Byron Williams loaded his car with firearms and ammunition and began driving west from his home in mountainous Groveland, California, toward San Francisco. Stopped on the way by a California highway patrol, he began shooting at them. He later told one of the officers that he had been planning to kill senior staffers at the Tides Foundation and the ACLU, in San Francisco. Williams was also a frequent watcher of Glenn Beck, who has singled out the little-known, progressive Tides Foundation for frequent attack on his program, but, interviewed in prison, Williams said he was not directly influenced by Beck.

Rep. Gabrielle Giffords was also the subject of frequent attacks by right wing politicians and commentators. Sarah Palin famously included her on a list of members of Congress to defeat politically, identifying them on a map with the symbol for a target used in shooting practice. This doesn't prove, though, that Palin or any other leader directly influenced Loughner, or helped to bring about his crimes.

FBI director Robert Mueller commented just after Loughner's attacks that the "ubiquitous nature of the Internet means that not only threats but also hate speech and other inciteful speech is much more readily available to individuals than quite clearly it was 8 or 10 or 15 years ago.  That absolutely presents a challenge for us, particularly when it results in what would be lone wolves or lone offenders undertaking attacks.”
Mueller is correct: inflammatory speech is a greater "challenge" than ever before - more pervasive, perhaps more influential - but it is still difficult to measure its influence on individual criminals or would-be criminals. Loughner, Wilson, and Williams are all apparently so unbalanced that their own testimony would not be probative. A more promising method would be to study their language for characteristic phrases that appear only in the speech or writings of others.