Facebook CEO Mark Zuckerberg
Facebook CEO Mark Zuckerberg. US Supreme is beginning to untangle what's legal to post on the mammoth social network site. Reuters

In a landmark decision that will have major ramifications for Facebook messages, the US Supreme court has overturned the conviction of a man serving time for posting threats on Facebook.

The court ruled overwhelmingly 7-2 that the test for a conviction is what the sender intends, not whether the recipient considers it a threat. The decision will make it far more difficult to prosecute online threats and hate speech.

The case involved Anthony Elonis, a Pennsylvania man who used Facebook to make a series of violent rants against his estranged wife and others beginning in 2010, often citing the rapper Eminem and using hip-hop lyrics, reports NBC.

He claimed his rants didn't amount to "true threats," and that his comments were "jokes" and a form of speech protected by the First Amendment.

Threats cause devastating harm to victims, including fear, anxiety, loss of sleep, and disruption, regardless of whether the abuser intended to threaten or only intended to vent or to make a joke
- Kim Gandy of the National Network to End Domestic Violence

In one post, Elonis said: "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."

Later, Elonis wondered whether a protective order his wife had obtained against him was "thick enough to stop a bullet." In another, he talked about initiating "the most heinous school shooting ever imagined."

He also posted that he had "enough explosives to take care of the state police and the sheriff's department."

Writing for the majority, Chief Justice John Roberts said a conviction for making criminal threats can't be based only on whether a reasonable person would regard communications as threatening. Instead, jurors must focus on the speakers' intentions; and a poster can be convicted if he intended to threaten someone or knew the communications would be viewed as a threat, Roberts added.

"What Elonis thinks does matter," Roberts wrote. Elonis's conviction doesn't stand because the jury didn't consider his state of mind when he made the Facebook posts, the court ruled.

Condemnation from anti-abuse groups

Advocates for victims of domestic violence condemned the ruling and said the court failed to recognise how terrifying social media threats can be.

"Threats cause devastating harm to victims, including fear, anxiety, loss of sleep, and disruption, regardless of whether the abuser intended to threaten or only intended to vent or to make a joke," Kim Gandy, president of the National Network to End Domestic Violence, told NBC.

The case attracted widespread interest because it was an opportunity for the court to define illegal internet speech. Free speech advocates argued that criminalising Facebook rants would create an unconstitutional chilling effect. Others argued that criminal penalties are appropriate in many cases especially as violent threats against women in particular skyrockets on social media.

The decision left the matter far from resolved.

In the dissenting opinion Justice Samuel Alito ripped the decision for offering little help in negotiating the law. "The court's disposition of this case is certain to cause confusion and serious problems. Lawyers and judges need to know which mental state is required for conviction," wrote Alito, who was joined in opposition by Justice Clarence Thomas. "This case squarely presents that issue, but the court provides only a partial answer."

Elonis' attorney said he's confident his client will be cleared when his case returns to a lower court.