Ferguson, Mo., police are investigating the stepfather of Michael Brown for possibly inciting a riot after he told a crowd to "burn this [expletive] down" immediately after learning that a police officer would not be indicted for shooting and killing his stepson.

In video reports from Ferguson, Brown's stepfather Louis Head, standing with Brown's mother and several others before an assembled crowd, can be heard saying multiple times, "Burn this [expletive] down." The video appears to have been taken moments after the Brown family learned of the grand jury's decision.

In the ensuing protests, which included both peaceful and violent elements and many hundred people, parts of Ferguson -- especially along West Florissant Avenue -- were engulfed with flames.

No charges have been filed against Head, but Ferguson Police Chief Tom Jackson told CNN that his department has "interviewed people who know Head and who were with him November 24 [the day the decision was announced]" in order to determine whether he intended any incitement.

Jackson has not classified the investigation, which he said includes multiple agencies, as formal, according to CNN.

Missouri Lt. Governor Peter Kinder said last week that Head "should be arrested and charged with inciting to riot." (Brown's mother and father, through their attorney, condemned Head's remarks.)

On Monday, Jackson told Fox News host Sean Hannity that the department's investigation would go beyond Head.

"Everyone who is responsible for taking away people's property, their livelihoods, their jobs, their businesses -- every single one of them needs to be prosecuted to the fullest extent of the law," Jackson said.

He said that Head has not yet been interviewed.

How could Louis Head be convicted?

This legal issue (at what point a call to violence becomes criminal) has come up before.

In its landmark 1969 ruling in Brandenburg v. Ohio, the United States Supreme Court defined the advocacy of violence, which is legal, from imminent lawless action.

In that case, assembled members of the Klu Klux Klan were recorded calling for "revengeance" against blacks and also called for a march on Washington, D.C., where both the president and Congress continued "to suppress the white, Caucasian race." A KKK leader, Clarence Brandenburg, was charged with advocating violence.

But the Supreme Court overturned his convinction, writing: "The constitutional guarantees of free speech and free press do not permit a State to forbid or proscribe advocacy of the use of force or of law violation except where such advocacy is directed to inciting or producing imminent lawless action and is likely to incite or produce such action."

The idea of "imminence" was further defined in 1973's Hess v. Indiana. In that case, Gregory Hess was appealing his arrest after being overheard calling for students at an anti-war rally to "take" a street from police. "We'll take the [expletive] street," he said, adding either the word "later" or "again."

Witnesses testified that Hess did not appear to be addressing a specific group or set of people within the crowd, did not speak any more loudly than other loud voices at the time and did not appear to be "exhorting the crowd to go back into the street."

The court found no rational basis for inferring that Hess' speech was likely and intended to incite violence from those around him.

Per Justia.com: The court held that Hess' speech "did not fall within any of the 'narrowly limited classes of speech' that the States may punish without violating the First and Fourteenth Amendments ... the evidence showed that the words he used were not directed to any person or group and there was no evidence that they were intended and likely to produce imminent disorder."

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This story has been updated.