A Milwaukee police officer shot an armed man to death on Saturday as he fled a traffic stop, spurring riots, violence, and familiar calls from protesters to end police brutality. But the Milwaukee shooting has a wrinkle that separates it from straightforward police executions like the alleged murder of Walter Scott: The victim, Sylville Smith, was apparently armed with a handgun as he fled the police. Did Smith’s firearm give the officer legal grounds to shoot him to death?

Probably not—but don’t expect the courts to say so. The struggle to define “reasonable” force against a suspect has bedeviled the justice system for decades, and the rules for deploying deadly force are even more vexing. Today, the standard that governs Smith’s killing is malleable enough to bend in any direction, and an attempt to sue the city or punish the officer for his conduct will be an uphill climb. But the Milwaukee shooting provides us with a brutal reminder that our modern problem of excessive police force cannot be curbed by current standards—and that Supreme Court Justice Sonia Sotomayor is on a quest to fix the faulty constitutional interpretation that led us into this mess in the first place.

That mess began with Tennessee v. Garner, a 1985 Supreme Court case that ostensibly limited officers’ ability to use deadly force. Using such force against a fleeing suspect—by, for instance, shooting him—constitutes a “seizure” of the person under the Fourth Amendment, the court reasoned. That meant the use of force may not be “unreasonable,” or else it violates the suspect’s constitutional rights. So what is the line between “reasonable” and unconstitutional? When “the suspect poses no immediate threat to the officer and no threat to others,” the majority held, “the harm resulting from failing to apprehend him does not justify the use of deadly force to do so.”

Unfortunately, Garner did not usher in a new era of enlightened policing, because just four years later, Chief Justice William Rehnquist—a Garner dissenter—effectively declawed the ruling with Graham v. Connor. In that decision, Rehnquist clarified that officers’ use of force need only be “objectively reasonable.” And who defines that standard? “The ‘reasonableness’ of a particular use of force,” Rehnquist wrote, “must be judged from the perspective of a reasonable officer on the scene, rather than with 20/20 vision of hindsight.” Moreover, “the ‘reasonableness’ inquiry in an excessive force case” must never examine an officer’s “underlying intent or motivation.” That means that if an officer shoots a suspect out of pure malice or extreme recklessness, but later explains why the shooting appeared justified in the moment, he acted within constitutional limits.

Rehnquist also gave lower courts a handful of vague factors they could cycle through before rotely concluding that “the totality of the circumstances” justified police officers’ dubious behavior. As the recent parade of failed and abandoned prosecutions against police officers demonstrates—and as myriad studies and analyses confirm—Rehnquist’s rewrite rendered the Garner principle basically toothless. Today, it’s nearly impossible to convict an officer for killing an unarmed fleeing suspect. When that suspect is armed—even if he hasn’t shot a single bullet or indicated that he will—both courts and cops often assume that any use of force, even against a suspect on the run, is “objectively reasonable.”

By the letter of the law, that common conjecture is incorrect. Yes, Garner involved an unarmed suspect, but it did not include a caveat declaring open season on armed fleeing suspects. And if we take Graham at face value, courts should evaluate whether the armed suspect “poses an immediate threat to the safety of the officers or others.” The fact that a suspect simply carried a gun while fleeing an officer does not irrefutably prove he posed an imminent threat to anybody. Indeed, fleeing the cops while being black and armed may, under the circumstances, seem like the most reasonable thing to do.

But just last term, the Supreme Court seemed willing to ratify this misreading of Garner by granting qualified immunity to an officer who shot a fleeing suspect to death under pretty shaky pretext. The decision, Mullenix v. Luna, centered around Texas state trooper Chadrin Mullenix, who was part of an operation meant to catch fugitive Israel Leija Jr., who was fleeing the police in a high-speed chase. Leija was allegedly armed and intoxicated; Mullenix was positioned on an overpass in view of spike strips designed to stop his vehicle. His supervisor told him not to use his weapon—but Mullenix did anyway, shooting Leija in the head, shoulders, and neck, and killing him. (“How’s that for proactive?” Mullenix later quipped to his supervisor.)

Eight justices concluded that Mullenix had not clearly violated the established constitutional rule governing deadly force. In a lone dissent, Justice Sonia Sotomayor berated her colleagues for abandoning Garner and rewriting the Fourth Amendment. When officers use deadly force, Sotomayor wrote, “the Fourth Amendment is violated unless the governmental interests in effectuating a particular kind of seizure outweigh the nature and quality of the intrusion on the individual’s Fourth Amendment interests.”

This prose doesn’t exactly sing, but Sotomayor then boils down her standard to a crystalline statement: “There must be a governmental interest not just in seizing a suspect, but in the level of force used to effectuate that seizure.” Put differently, officers may not deploy deadly force just because a fleeing suspect might be dangerous; if they have another means of seizing the suspect, in Sotomayor’s view, a court must consider why they didn’t use it. When a court instead allows officers to ignore less lethal alternatives, Sotomayor wrote, it sanctions “a ‘shoot first, think later’ approach to policing.”

“Shoot first, think later” appears to be a fairly apt description of the killing of Sylville Smith. According to an account of police body-camera footage, officers ordered Smith to drop his gun as he was fleeing; when he did not, he was shot to death. If Sotomayor’s views found a majority on the court, the officer’s actions might be properly investigated as an “unreasonable” killing. But for now, Sotomayor remains in dissent. And that means Smith’s death will likely result in a cursory investigation, no penalties for the officer involved, and no justice for anyone.