Washington (CNN) The Supreme Court declined Monday to take up the case of rapper Jamal Knox, who argued he was sent to prison for a song that was protected by the First Amendment.

By avoiding the issue for now, the justices left for another day a look at the contours of so called "true threats" -- speech that falls outside the protections of the First Amendment.

The case was of keen interest to rappers who weighed in to argue that rap music is a "work of poetry" where "meter and rhyme are primary," and words are often chosen for their contribution to a song's rhythm rather than its precise message.

In a legal brief filed in early March, rappers Killer Mike, Chance the Rapper, Meek Mill, Yo Gotti, Fat Joe and 21 Savage were among a group of artists and scholars who say Knox's rap song "F*** the Police" is a "political statement ... that no reasonable person familiar with rap music would have interpreted as a true threat of violence."

Following a 2012 arrest in part for gun and drug charges, Knox, who performs under the moniker "Mayhem Mal," and Rashee Beasley, who goes by "Souja Beaz," wrote and recorded a song titled, "F*** the Police," seen as a homage to the N.W.A. 1988 rap song "F*** tha Police." Knox and Beasley's song, posted on Facebook and YouTube, included the names of the two Pittsburgh officers who arrested them with lyrics like, "I'ma jam this rusty knife all in his guts and chop his feet" and "Well your shift over at three and I'm gonna f*** up where you sleep."

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