HARRISBURG — The lawyer for a Pittsburgh rapper challenging his conviction over a music video that referenced violence against police officers told state Supreme Court justices Tuesday that his client's speech was a form of art protected by the First Amendment.

But an attorney for prosecutors said Jamal Knox's choice to name two officers who arrested him and include the words, "Let's kill these cops, cause they don't do us no good…" went too far.

"We're all for cathartic relief. We're all for self-expression," said Franceso Nepa, an Allegheny County assistant district attorney. But, he argued, "You can't say the things that Mr. Knox says in the video…It's going too far."

Nepa urged the seven justices to reject a petition by Knox's lawyers to vacate the 23-year-old's conviction on threatening officers.

During less than an hour of argument, the court offered few clues as to which way it was leaning and none about when it will rule. Some justices asked many questions, while others remained largely quiet. But the free-speech issues at stake in case mean it could be ripe for an appeal to the U.S. Supreme Court.

Knox has already served prison time in the case. He and his co-defendant, Rashee Beasley, 26, were convicted of terroristic threats for recording the rap song, referred to in court filings as "F— the Police," in 2012.

Knox's attorney, Mikhail Pappas, argued Tuesday that his client did not meet the legal standards for communicating a threat, in part, because he did not deliver it directly to the officers. Based on data found through search warrants on cell providers, the defense lawyers maintained that a third person posted the rap video on social media, where Pittsburgh police discovered it.

Justice David Wecht popped back with a Chaucer quote: "What's saidth is seeith and there it goes" — suggesting that once he made the video, Knox should have expected it be shared or seen.

Even the justices seemed at times to disagree about whether the way police discovered the rap video was crucial to whether it met the definition of a threat or whether the lyrics were more important.

"There is a freedom to offend," Wecht said at one point, "but there is no freedom to threaten."

Pappas argued that threats in rap "are ubiquitous." He said that his client's track record as a musician was well-known by police — he didn't claim to be a rapper only after his arrest — supporting the idea that his client's video should be viewed as art.

For Wecht, that seemed like a slippery slope. "Was Michelangelo not an artist at the time of his first creation?" the justice asked.

Justice Christine Donohue asked whether Knox needed to understand that his video would be viewed by police to fit the legal definition of a threat.

Nepa said: "Just the fact that he put it on the Facebook page — it was a Facebook page that had unlimited access — I think that is sufficient."