Saying that someone deserves to be killed certainly gets anyone’s attention.

But when does saying that or something like it pass from just being hateful speech that offends, or just so much hot air, to what the law calls a “true threat” — and the catalyst for criminal prosecution?

For a Florida rapper, the lyrics he wrote for the song “Kill Me A Cop” recently resulted in a two-year prison term. And a New Jersey blogger, who sometimes hosts an Internet radio talk show, faces federal and state charges in Connecticut and Illinois for several Web postings in June.

Both cases raise questions about where the line will be drawn in today’s society — beset by the ongoing war on terror and shocked by all-too-frequent killings in small towns and big cities — on our freedom to speak freely even in harsh and offensive ways.

Court decisions stretching back to the 1960s offer some guidelines for us and for prosecutors in measuring whether our words are protected or not. A threatening statement can cross that legal line when it’s made or relayed directly to a person and when there’s a reasonable chance the threat can be carried out in an immediate, “imminent” way.

How might those guidelines apply to the rapper and the blogger?

The Associated Press reported that Antavio Johnson pleaded “no contest” in July to threatening two Lakeland, Fla., police officers in a song he wrote, telling a detective while he was in jail on a drug charge that he had felt harassed by the officers. First Amendment advocates said the case raised the issue of whether you can be prosecuted just for expressing ideas, however repellent, rather than actions.

Johnson’s lawyer said he was just “blowing off steam” when he wrote lyrics that included the line, “I’m-ma kill me a cop one day.” But a local prosecutor said that by naming the two officers, the song entered a realm where “there were specific threats made to specific people.”

Federal authorities in Chicago say blogger Hal Turner was even more specific in what they say he posted online directed at three federal judges: “Let me be the first to say this plainly: These judges deserve to be killed,” and “Observe the Constitution or die.” The trio had recently upheld laws banning handguns in two Illinois cities.

The charge against Turner says he also posted the names, photos, phone numbers, work addresses and office room numbers of the three judges; a photo and map of the federal courthouse in Chicago where they sit; and promised to provide home addresses and maps for each.

Turner’s case has some echoes of a dispute that began in 1997 around a Web site named “The Nuremberg Files.” That site posted the names, photos and addresses of staff at clinics where abortions were performed. When anyone on the list was killed or wounded, the name was crossed off or shaded. In 2008, the U.S. Supreme Court refused to review a $4.7 million damages award to a group of doctors who had sued the site’s operators in 1999. At one point during the lengthy appeals, the site was deemed a “true threat” by a federal judge, though no criminal charges were involved.

Just a few days ago, Turner’s attorney added a strange twist to the case — saying that Turner was an “agent provocateur” for the FBI for several years and had been instructed by agents on “what he could say that wouldn’t be crossing the line” about people in the right-wing groups he infiltrated — and that what Turner said about the judges was no different.

Nothing in the 45 words of the First Amendment says we cannot be impolite, argumentative, insulting, even vile. Real threats to life and limb, whether we sing, say or post the words, are not protected speech. Johnson’s case is over, and for Turner the distinction between protected speech and a true threat will be determined in court. But we should expect — and protect — vigorous debate over serious public issues, which may well provoke tempers as well as intemperate remarks.

Gene Policinski is vice president and executive director of the First Amendment Center, 555 Pennsylvania Ave., Washington, D.C., 20001. Web: www.firstamendmentcenter.org. E-mail:gpolicinski@fac.org .