(CNN) As with so many similar cases, those protesting the killing of Alton Sterling believe they've seen enough to draw the conclusion that he died at the hands of overzealous police.
This is based on a video that appears to show two officers wrestling Sterling to the ground and restraining him before gunshots erupt.
Put aside the lengthy debate that will inevitably ensue, and there are at least two facts on which everyone agrees: Baton Rouge, Louisiana, police say they were responding to a report of a man brandishing a gun, and Sterling died of multiple gunshot wounds after an altercation with police.
More police shootings, or more coverage?
Demonstrators are quick to call the killing extrajudicial -- and certainly, state and federal authorities will make that call -- but guiding investigators will be a seemingly simple but key query: Did officers believe their use of force was justified?
Since the 2014 death of Michael Brown in Ferguson, Missouri, the United States has kept a keen eye on police killings.
In turn, it has received an education in how the justice system treats these cases.
It's common to hear those outraged by police behavior claim that cops too often skate in these instances, and without debating the merits of that assertion, it's important to examine the guideposts that the Supreme Court put in place in the 1980s.
Via two decisions, which we'll dig into here, the Supreme Court set the bar in such a place that a police officer can open fire if she or he believes the suspect poses a threat to the officer or the community. That's from the 1985 decision in Tennessee v. Garner.
At the same time, the court has granted officers -- based on the circumstances and their states of mind at the time of the arrest -- significant leeway in dictating whether a use of force was justified. That ruling came four years later in Graham v. Connor.
In the '70s, Tennessee had a law providing that the police could employ "all the necessary means to effect the arrest." So, when two Memphis policemen responding to a prowler call encountered 15-year-old Edward Garner climbing a fence as he fled a home that he was suspected of burglarizing, Officer Elton Hymon opened fire.
Garner died at the hospital. In his possession was no weapon, but $10 and a stolen purse. Garner's father sued, alleging numerous constitutional violations. The case traversed the courts for more than a decade before the Supreme Court issued its landmark ruling.
That the Tennessee statute mandating use of force was unconstitutional. For the purposes of this discussion, here is the operative paragraph:
"Where the suspect poses no immediate threat to the officer and no threat to others, the harm resulting from failing to apprehend him does not justify the use of deadly force to do so. It is no doubt unfortunate when a suspect who is in sight escapes, but the fact that the police arrive a little late or are a little slower afoot does not always justify killing the suspect. A police officer may not seize an unarmed, nondangerous suspect by shooting him dead."
That's an oversimplified translation, and it omits the now-important variable that is the officer's belief at the time of the apprehension.
This is where Graham v. Connor comes in. That case began in 1983 when Dethorne Graham, a diabetic, asked a friend to take him to a Charlotte, North Carolina, store for orange juice to counteract an insulin reaction. The line in the store was long, so Graham walked in and quickly exited, drawing the suspicion of Officer M.S. Connor.
Graham asked his friend to take him to his girlfriend's house for orange juice, and as the pair left, Connor followed, pulling them over a short distance from the store. Suffering from the reaction, Graham acted strangely, exited the car, circled it twice and sat down on the curb before passing out.
Graham was handcuffed and when backup officers arrived, one thought he was drunk. He was placed over the hood, and as Graham pleaded with officers to pull the diabetic information from his wallet, one of the officers told him to shut up and shoved his head down. Graham filed suit, saying he'd suffered injuries, including a broken foot, during the stop.
Hindsight is 20/20, right? Well, an officer's split-second decision-making during a heated moment is not. Enter the "objective reasonableness" standard, by which police use of force is measured today.
Citing the 1973 federal appeals court decision in Johnson v. Glick, the court noted that not "every push or shove" is excessive, "even if it may later seem unnecessary in the peace of a judge's chambers."
The ruling continued, "The calculus of reasonableness must embody allowance for the fact that police officers are often forced to make split-second judgments -- in circumstances that are tense, uncertain, and rapidly evolving -- about the amount of force that is necessary in a particular situation."
As mentioned earlier, there are still many unknowns in the Sterling case. While the video certainly appears to show the officers killing Sterling, it fails to illuminate other details, namely whether Sterling was armed and posed a threat to officers.
Those details may be forthcoming when witness accounts, dashcam video, police body camera audio and surveillance video from the store are released.
East Baton Rouge District Attorney Hillar Moore said Wednesday the U.S. Justice Department had asked him to "stand down" as it conducts an investigation, but he noted this case will be handled differently than shootings that don't involve police. Law enforcement, he said, have the authority to use deadly force in certain situations.
"This is a potentially state-authorized killing," he said. "It gives law enforcement officers the authority and mandates them to kill when in defense of themselves or others."
According to the latest report available from the Internal Affairs Office at the Baton Rouge Police Department, 35 "use of force" cases were reported to the department in 2014. None resulted in charges against the police officers involved.
In most cases, "there was insufficient evidence to either sustain the complaint or exonerate the officer," the report said. Officers were cleared in 12 cases and several cases remained pending at the end of 2014.