A grand jury’s decision not to bring charges against Ferguson Police Officer Darren Wilson hinged on the threat he perceived when he shot and killed Michael Brown, Professor Lisa McElroy observed in an op-ed published in the Los Angeles Times on Dec. 2.

On Dec. 1, McElroy noted, the U.S. Supreme Court heard arguments in the case of Pennsylvania resident Anthony Elonis, whose facebook messages were found by a jury to pose a true threat to his estranged wife.

“The Ferguson situation and the case before the high court revolve around the question of whether the recipient of a communication should be the determiner of whether that message or conduct is a threat,” McElroy wrote.

Previous Supreme Court decisions have upheld the rights of police officers to make reasonable decisions about threats they face, even if those decisions are not proven to be correct, McElroy said.

In the Elonis case, McElroy observed, the court must decide if the First Amendment protects a person’s declared goal of expressing anger or if the fear that the target of an ominous message perceives represents a true threat not covered by free-speech rights.

Elonis’ argument, that prosecutors needed to prove he actually intended to threaten his wife or to elicit fear on her part, would be very hard to prove, McElroy said during a Dec. 1 interview on Southern California Public Radio station KPCC.

Noting that First Amendment cases tend not to split the Supreme Court on ideological lines, McElroy said that a transcript of the Dec. 1 arguments suggested that “the justices were really struggling with this.”