he spotted the cigars: chief struggley set the stage for darren "barney fife" wilson to walk...,

vox |  In the 1980s, a pair of Supreme Court decisions set up a framework for determining when deadly force by cops is reasonable. Those decisions have governed how state laws are applied. Furthermore, many agencies simply use identical standards to the Supreme Court's for their own use-of-force policies — though some departments don't let officers use deadly force even when the Court decisions say they'd be allowed to.

Constitutionally, "police officers are allowed to shoot under two circumstances," says Klinger. The first circumstance is "to protect their life or the life of another innocent party" — what departments call the "defense-of-life" standard. The second circumstance is to prevent a suspect from escaping, but only if the officer has probable cause to think the suspect's committed a serious violent felony.

cops can't shoot every felon who tries to escape

The logic behind the second circumstance, says Klinger, comes from a Supreme Court decision called Tennessee vs. Garner. That case involved a pair of police officers who shot a 15-year-old boy as he fled from a burglary. (He'd stolen $10 and a purse from a house.) The Court ruled that cops couldn't shoot every felon who tried to escape. But, as Klinger says, "they basically say that the job of a cop is to protect people from violence, and if you've got a violent person who's fleeing, you can shoot them to stop their flight."

Some police departments' policies only allow deadly force in the first circumstance: defense of life. Others have policies that also allow deadly force to prevent escape in certain cases, within the limits of the Supreme Court decision.

Does the convenience store robbery matter?

Shortly after releasing the documents that identified Brown as the primary suspect in a convenience-store robbery, the Ferguson Police Department clarified that Wilson had not known that Brown was a robbery suspect when he made "initial contact" with Brown and his friend Dorian Johnson. (Instead, the department says, Wilson stopped the teenagers because they were walking in the middle of the street.)

That phrasing doesn't make it clear whether or not Wilson believed Brown to be a robbery suspect when he started to shoot at him. If he did, it might then be up to the investigators and county prosecutor McCulloch to decide whether a "strong-arm robbery," as the Ferguson Police Department described the incident, counts as a violent felony. If they decide it does, that will go some way toward a legal justification for Wilson's action. On the other hand, Wilson would only be able to claim that he was justified if Brown was fleeing — which eyewitnesses say he wasn't.

It's most likely, however, that the whole question is moot. From the Ferguson Police Department's statements on the afternoon of August 15th, it doesn't sound like Wilson even knew about the robbery at all. In that case, there's no way for him to claim that he was justified in keeping a violent felon from fleeing, because he didn't even know Brown was a suspect in a crime at all.

Wilson could instead, however, claim "defense of life" — that he feared for his life when Brown (according to his story) assaulted him in his car. In that case, the next question will be whether it was reasonable for him to be afraid of Brown.