The Supreme Court on Monday inched a little bit closer to answering a major free-speech question: how to draw the line between real threats of violence and angry diatribes protected by the First Amendment.

In an 8-1 ruling, the Court threw out the conviction of a Pennsylvania man who wrote violent, obscene Facebook posts about killing his wife, his coworkers, FBI agents, and even kindergartners. But the Court did not set a clear standard for future cases involving online threats, and some of the justices complained that the ruling would only make the legal landscape more complicated.

"Our job is to decide questions, not create them," Justice Clarence Thomas said in a dissenting opinion.

The Court's ruling will make it harder to prosecute people for their social-media messages—but it's not clear what, exactly, prosecutors will have to prove.

Elonis v. United States has been one of the most highly anticipated cases of the term, in large part because legal experts saw in it potentially profound First Amendment implications. But the Court stayed far away from any constitutional issues in Monday's ruling, focusing instead on the legal standards applied in Anthony Elonis's trial.

Elonis's legal troubles started after his wife left him in 2010. He started posting angry, violent messages about killing her. "I'm not going to rest until your body is a mess, soaked in blood and dying from all the little cuts," he wrote in one post. Some of his messages took the form of song lyrics—for example, the one about a female FBI agent investigating his case: "Leave her bleedin' from her jugular in the arms of her partner."

He was ultimately convicted of transmitting threats. To win that conviction, prosecutors needed to prove that a statement was a true threat—not just talk. And the standards for establishing a "true threat" were at the center of Elonis's appeal to the Supreme Court.

Elonis said he never intended to do any of the things he wrote about online, so his posts should be protected under the First Amendment.

But when he was convicted, the jury was instructed not to worry about Elonis's intent. Rather, the jurors were told to determine whether a "reasonable person" would expect the statements to be interpreted as threats.

That standard wasn't good enough, Chief Justice John Roberts said Monday.

"Federal criminal liability generally does not turn solely on the results of an act without considering the defendant's mental state," Roberts wrote.

Roberts said the intent of the person who makes a statement has to be a factor—but he didn't say how much weight it should carry, or which specific legal standard prosecutors have to meet.

Justice Samuel Alito agreed with part of the majority's ruling but said it should have answered those questions. Lower courts will be stuck with "confusion and serious problems" as they try to apply Monday's ruling, Alito said in his opinion.

"The Court refuses to explain what type of intent was necessary," Alito wrote. "Did the jury need to find that Elonis had the purpose of conveying a true threat? Was it enough if he knew that his words conveyed such a threat? Would recklessness suffice? The Court declines to say. Attorneys and judges are left to guess."

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