The police killing of an unarmed 19-year-old on a Brooklyn rooftop last month appears to be a tragedy of nanoseconds and eons, a death delivered by a cop firing not because of a conscious decision but an instantaneous neuronal impulse hardwired from the days of our animal ancestors.

And there’s an obvious subtext of race. The shooter, officer Richard S. Neri Jr., is white. The victim, Timothy Stansbury Jr., was black. Scientific research has a say here too, probing whether our rawest reflexes can be primed by modern fears based on race.

Scientists are intensely studying the amygdala, a pair of almond-shaped neuron clusters inside the brain, to understand its role in post-traumatic stress disorder. The amygdala encodes memory with emotional weight, but it also alerts us to sensory information that we associate with danger. It’s the jittery small mammal inside us, always awaiting loud noises, sudden movements, and glints of teeth. The more we expect a threat, the more excitable it becomes.

Our three responses to a scare are the same as they are for any animal: fight, flee, or most commonly, freeze. But we expect cops to be a different breed. How successfully Neri was transformed into that breed may become the subject of a grand jury hearing for criminal negligence.

“We try to train the freeze response out of police, because if they freeze, they could be killed,” said Alexis Artwohl, a retired police psychologist and consultant to law enforcement agencies. And, she added, “We also don’t pay cops to run away.”

A rooftop affords neither distance nor cover to a cop in danger. Those at projects like the Louis Armstrong Houses in Bedford-Stuyvesant, where the shooting occurred, are sometimes the roosts of rapists and drug dealers and their pit bulls. Neri and his partner, Jason Hallik, were on the edge of fight in the 1 a.m. darkness and cold. Like many officers, they walked “vertical patrol,” leaving the street and climbing to the upper stories, with guns drawn.

Inside the complex, Stansbury and two of his friends were happily bounding up the well-lit stairwell. They intended to cross between buildings to a birthday party, using the linked roofs as a skyway.

Neither of the two people at the center of this tragedy would seem to have had anything to fear from the other. Stansbury, a student who worked at McDonald’s, wasn’t a threat to Neri. He was unarmed and didn’t have a record. And Neri doesn’t seem like the kind of white cop who haunts the nightmares of young black men. In his 11 years on the job, he’d never fired his gun or received a civilian complaint. Yet the door opened, the gun fired, and the mortally wounded Stansbury fell back into his friends, stumbling away with the life gushing out of him.

What went wrong in that terrifying and bewildering moment was a signal that leapt from dendrite to dendrite in a wordless flash. Press reports have called the fatal blast an accidental shooting, which brings to mind the cavalier handling of a firearm, or feckless gun cleaning. But neurological research suggests that the problem is much deeper, and that such shootings may be almost impossible to eliminate.

“I think it is important to distinguish between discharges that are accidental and those that are unintentional,” said Roger M. Enoka, chair of the department of integrative physiology at the University of Colorado. “An accidental discharge occurs when a weapon is not being handled correctly. In contrast, an unintentional discharge occurs when a physiological response causes the trigger to be depressed while the gun is being handled in an appropriate manner.”

Many analyses have mentioned the startle response—that wave of muscle contractions starting with an eye blink and extending to clutching hands—as a possible culprit in the Neri case. But in a recent paper for Law Enforcement Executive Forum, Enoka raises another intriguing idea. Our brain has a near compulsion for symmetry. When a signal is sent to one limb, a doppelgänger signal spills over to the other. This phenomenon is so powerful that Shi Zhou, a physiologist at Southern Cross University in Australia, reported to Exercise and Sports Sciences Reviews that limbs opposite to those being exercised also gained substantial strength.

Police trainers have witnessed this cross-wiring in what they call “sympathetic contractions” and physiologists call “mirror movement” or “contralateral irradiation.” An intended action with one hand is matched by a weaker echo in the other.

William Lewinski, a police psychologist at Minnesota State University, remarked, “We’ve got a police officer here in Minnesota without a thumb because as he was squeezing handcuffs closed on a suspect, he blew his own thumb off. It’s a seepage of neural impulses across the corpus callosum,” a thick band of nerve fibers bridging the hemispheres of the brain.

It’s not clear who opened the rooftop door, but if Neri did, that could help explain what went wrong. “The action of opening a door with one hand can be sufficient to evoke a sympathetic contraction that is strong enough to cause the fingers in the other hand to squeeze the trigger and discharge a gun,” Enoka said.

The fact that Neri was likely to be tense, on alert, makes that kind of misfire more likely, because it could have ratcheted up the startle response, Enoka observed. “The physiological responses that cause an unintentional discharge—sympathetic contraction, loss of balance, and startle reaction—are all enhanced when an individual is aroused,” he said.

To Lewinski, who is sometimes called as a defense witness for police officers on trial, what happened in Neri’s brain could have been something like a perfect storm. “He goes to the door anticipating danger, squeezes the door handle, which causes a contralateral contraction. Maybe there’s a push and pull simultaneously at the door, which startles him, and the gun goes off. Oh, God,” he said.

That despair is too familiar in New York City. This week marks the fifth anniversary of the killing by four New York City cops of Amadou Diallo. That 22-year-old African immigrant went down in a hail of 41 bullets, 19 of which hit him. Despite the reductive parallels of a black young man’s being killed by a white cop’s bullet, the cases aren’t really the same. Neri shot once, and his partner didn’t fire at all. Yet was race still a factor?

To investigate this possibility isn’t to label Neri a racist cop—it’s just likely that he carries some burden of prejudice, as pretty much all of us do.

“You give me a perfect society to draw recruits from and I’ll give you a perfect police officer,” said James O’Keefe, a professor of criminal justice at St. John’s University who was director of training at the New York Police Department Academy until late 2001.

Data from recent neurological and psychological studies compel us again to return to the amygdala. NYU neuroscientist Elizabeth Phelps was the co-author of a study that looked at the relationship between racial bias, the startle response, and amygdala activation. Test subjects were exposed to loud noises while viewing photos of black or white people. Magnetic resonance imaging scanners recorded the effect on their brains. What she found, according to an interview with the W.W. Norton website Psychological Science, “was that most [white subjects]—though not all—showed greater amygdala activation to the Black faces than the White faces.”

Other studies have demonstrated that higher thinking slows in response to a cross-racial stimulus, and that the amygdala response to other races is seen in black subjects too. Indeed, it may be a reaction to novelty, not fear, and if so, it could subside with exposure. The amygdala, so central to memory, naturally plays a part in how we acquire new fears, sometimes based on misperceptions. And even there, on the neuronal level, such fears can be eased as well. We know too little to conclude that Neri himself was afraid of black people.

“These police officers experience the community eight hours a day. They don’t just meet minority perps, they meet minority victims and minority members of the neighborhood. I think they’re probably less inclined to see things in racial terms than the average joe and more comfortable where they are than somebody whose car broke down near the projects,” O’Keefe said. “A lot of people are attributing what happened to fear. I don’t buy that for a second.”

But other psychological tests certainly indicate the power of misjudgment, if not fear. A recent University of Wisconsin study found that “an automatic association was observed between Black faces and weapons.” White subjects were shown photos of white faces and black faces, and then given flashes of images to identify as guns or tools. They were slower to correctly identify a tool when the image was associated with a black face, and more often wrongly identified a tool as a gun.

The authors of these studies weren’t eager to step into the current firestorm. Phelps and others declined to comment, saying further research was needed. Some didn’t reply to repeated calls and e-mails at all.

Even if neuroscience can positively link the amygdala to unconscious racial bias and the startle reaction, don’t look to the lab for solutions any time soon.

Neuroscientist Gregory Quirk, with the Ponce School of Medicine in Puerto Rico, studies fear extinction in rats by stimulating the prefrontal cortex. “In the future we might want to do something with people to help them overcome things that could traumatize them, so they will not be afraid of stimuli they are likely to encounter,” he said. “But that is way far off into the future.”

And recent studies on Tibetan Buddhist monks demonstrating that meditation can calm the amygdala offer little comfort for police officers or those who interact with them. “That might work for a monk in the relative safety of a monastery, but not an officer on a rooftop at 1:30,” O’Keefe said of the techniques. “Even if I could do that, as a trainer I don’t think I would want to. That animal instinct and survival mechanism is what keeps cops safe. That’s what gets them home at night.”

The solutions offered by experts interviewed for this article are more prosaic. They hit repeatedly on the same conclusions: offering frequent training in realistic scenarios and having cops carry guns with their fingers on the frame, not the trigger. But Lewinski acknowledged that simply placing a finger away from the trigger could cost a cop his life. Hundredths of a second count, he said.

But we don’t think rationally in hundredths of a second. The goal of tactics must be to buy time and the chance for communication, O’Keefe said. “Technology could help in this area, if it can be developed in an affordable way.” He advocated the use of portable thermal imaging scanners, which can see body heat through barriers, to let cops glimpse what’s behind doors before they open them.

It’s tempting to daydream of how that night might have been different had Neri and Hallik been equipped with such a camera, watching the heat outline of Stansbury’s lanky frame heading up to the winter night, ablaze with life. They wait and watch to see what kind of young man emerges from the stairwell, the element of fearful surprise all but extinguished. One can imagine words—there would be time for words.

“Hey, kid! Go back downstairs,” they might have said. “Don’t you know the roof can be dangerous?” It was dangerous, for Stansbury. He died, and now it’s up to the courts, not scientists, to determine whether Neri should be held responsible.