But the court took pains to make its ruling on statutory grounds rather than address the broader issue of whether such a statement is protected under First Amendment guarantees of free speech.
The nine-member court first heard arguments in the case December 1, 2014. The panel had to rule on apparent death threats that a man upset over his separation from his wife made against her on Facebook. His comments landed him in prison.
Elonis was convicted of violating a federal law that makes it a crime to transmit in interstate commerce "any communication containing any threat . . . to injure the person of another."
"There's one way to love you but a thousand ways to kill you. I'm not going to rest until your body is a mess, soaked in blood and dying from all the little cuts," Anthony Elonis' post said in the form of rap music lyrics.
The court had to decide if the threat posted on Facebook actually bore with it an intention to cause harm or was rather a form of expression covered by the First Amendment.
In a 7-2 decision, the judges said it was "unnecessary to consider any 1st Amendment issues."
It said "requiring only negligence with respect to the communication of a threat is not sufficient to support a conviction."
Elonis has said that his post was simply a "therapeutic" tool and that he had no intention to hurt anyone, so his message did not amount to an actual threat.
Still, a lower court sentenced him to three years in jail and three years' probation.
But the Supreme Court sided Monday with Elonis. It threw out his conviction and sent the case back to the lower court.
The high court said prosecutors should have had to prove that Elonis actually had a specific intent to cause harm to his estranged wife.
When the case first came before the court late last year, the government had argued that the federal law under which Elonis was jailed barred actual threats defined as statements a "reasonable person" would construe as the serious expression of an intent to cause harm.
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