On a Thursday in late November, the entire indomitable city of New Orleans recoiled in shared horror at security video of a young medical student collapsed on the sidewalk just off Magazine Street, clutching his bleeding torso, as a hooded assailant stood over him with a gun aimed at his head. The film’s dreadful silence only amplified the menace as the gunman apparently tried to squeeze the trigger, twice, to finish off his already-incapacitated victim, giving up only when a mechanical mercy intervened and the gun refused to fire.

Two nights later, Bunny Friend park in the Ninth Ward — its almost comically benign name a memorial to a teen who died in an accident in the 1920s — became the scene of the city’s next headline-grabbing gun battle. A block party and planned music-video shoot were rent apart by a hail of gunfire, leaving 17 people wounded, and at least a half dozen people have been named as suspects as investigators try to piece together how the celebration turned to chaos.

The bloodshed continued the following weekend, when more young men’s lives would be claimed around some of the city’s most best-known places: 26-year-old Brandon Robinson killed on Bourbon Street, 19-year-old Richad Dowell on Canal Street and 19-year-old Devin Johnson near the newly opened Lafitte Greenway.

And yet, city officials continue to insist that the struggle against violent crime in New Orleans has made significant strides in recent years, and many measurements as well as newly-published academic studies back them up. But if things are getting better, why does the carnage still insist on making its way onto playgrounds, green spaces and tourist thoroughfares? If the violence is the work of a relatively small group of people, why are they so hard to stop?

The answer to all those questions, experts say, may lie in a relatively new understanding of violence itself as a disease – not only in a rhetorical sense, but in the mechanism by which it festers and spreads in a community like an infection through the body. And the only way to treat the terrifying symptoms playing out in the public eye, those officials say, is to continue treating this disease at its origins.

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For a large swath of the city’s population, violence is a health threat in a strictly literal sense, as it claims more lives than any disease. Homicide is the fourth highest cause of death in this city each year, behind cancer, heart disease and accidents. For the United States as a whole, by contrast, homicide is such an uncommon cause of death that it doesn’t rank in the top 15. Those homicide deaths in New Orleans are almost strictly limited to the black population, however, and for black people between the ages of 5 and 44 (comprising 45 percent of the city’s population) homicide is by far the leading cause of death.

Those killings are likewise concentrated in certain areas in the city, well known to officials and the public alike – Central City and Hollygrove, Treme and the Seventh Ward, New Orleans East, parts of Algiers. This pattern, a handful of neighborhoods with homicide problems that far outpace the rest of the city, is repeated in urban areas across the country, said Charles West, who as the city’s innovation director leads the new anti-violence initiatives.

“There are about three or four neighborhoods in New Orleans that we refer to as our hotspots that have significantly higher incidents of violence. But if you look at every major city, even those that have much lower murder rates, there are about three or four neighborhoods that have incidents of murders that are about four times that city’s average,” West said. Those neighborhoods all share the same factors — unemployment twice the city’s average, educational attainment half the city’s average, babies with low birth weights, and high infant mortality rates. “All of the same things you look at from a public health standpoint, you overlay them, and they exactly overlap with these neighborhoods.”

When such neat lines can be drawn around the violence, it is becomes absurdly easy for the rest of the city to look away, to treat the violence as another neighborhood’s problem, even when that other neighborhood is only a stone’s throw away. In late October – midway between the bloodless Uptown restaurant robberies that seized the city with fear and outrage and November’s outbreak of headline-grabbing bloodshed – two businesses on South Claiborne, a barber shop and daiquiri bar, were robbed at gunpoint by masked men. Unlike at the restaurants, however, the business owners and employees were terrified to speak about their ordeals. Even after the suspects were arrested, workers feared being targeted for retribution for even being seen taking a reporter’s business card. Anyone could be right around, they insisted, watching at that very moment.

Meanwhile, although the crimes were strikingly similar — businesses robbed during operating hours, their patrons forced to the floor at gunpoint — no mayoral news conferences or City Council hearings followed, and no mounted patrols were assigned to South Claiborne. No lines formed of patrons packing the seats in a show of solidarity, no news vans or cameras lined the street, and the articles that were written about the incidents drew paltry reader interest — even though the crimes took place within sight of the lauded Magnolia Marketplace development with a gleaming new Raising Cane’s out front.

The disparity in public attention to crimes based on the neighborhoods where they occur is reminiscent of a leper colony — a “medieval” approach to dealing with the problem, said state Sen. J.P. Morrell. People in safe areas might pity those near the source of infection, but their primary hope is that the disease doesn’t spread to them.

“For communities that are struggling with violence and a violent culture, the lack of police presence and a lack of resources makes it difficult to overcome what already exists,” Morrell said. “When you talk to people from these communities, the common thing you always hear is that ‘The city has forgotten about us.’ That hopelessness breeds that perpetual ongoing resurgence of crime.”

That lack of a shared investment in all crimes can perpetuate the system of street justice, experts say, which in turn fuels further violence. Even if the crime is solved by police, the grievances and disputes around it persist in the neighborhood, and the ongoing pattern of violence and retaliation from the streets remains more real and tangible to its victims than any notion of protection from the “system.” Researchers describe that fear as an expression of a lack of “police legitimacy” – the system of laws and enforcement as it is known to the law-abiding public has less sway in some communities than the constant cycle of street justice.

Any detective, meanwhile, would say that the crimes in the city’s hotspots have a direct connection to those committed elsewhere — because if criminals can get away with knocking over a barber shop or corner store, there is little doubt that they may consider trying a more lucrative target in a “better” area next. And others on the street say that while the suspects are behind bars, those kinds of acts of violence live on – anyone in the neighborhood upset by the affront that the robberies represent may yet be planning retaliation.

Like a virus or an infection, the violent act perpetuates itself and spreads.

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In 2013, the city actually made a significant dent in the violence, dropping from just under 200 homicides in 2012 to 155 in 2013, a figure that held steady in 2014 and seems roughly on pace to do so again in 2015. That 20-percent decrease, according to a study by two University of Cincinnati professors just published in August of this year in the journal “Criminology & Public Policy,” has a clear and statistically significant cause – not the folk tales of better emergency medicine or some aberration in the accuracy of the shooters — but a new form of targeted intervention specifically against the individuals involved that has shown similar repeatable results in not only New Orleans but also a number of other urban areas.

The new concept, known as the Group Violence Reduction Strategy, begins with intelligence gathering. In 2012, police identified 59 street-level neighborhood gangs totaling about 600 or 700 members, though the structure is loose and subject to continual change in membership. Previous reviews — back when “New Orleans doesn’t have gangs” was a police mantra — identified 2 percent of homicides or fewer as gang-related, but through this new lens led to classifying nearly 55 percent of homicides as involving gang members. Police detectives then compile all the information they can gather on people involved in violent crimes — whom they are related to, whom they’ve been stopped with, whom they interact with on social media, what shootings they’ve been witnesses to, what cars they’ve been in, and what guns they’ve been connected to — and literally construct social networks mapping relationships among people involved in violence.

Armed with that information, police and city officials then summon the individuals involved in the most active gangs into a courtroom – usually 10 to 15 who are already in jail for other infractions, and about 30 on parole or probation – and describe to them how much the police know about them and their networks. The entire law enforcement community — police brass and detectives, state and federal prosecutors, the mayor — sit on one side of the courtroom, and the representatives of nonprofits and education agencies sit on the other, presenting these high-risk offenders with a clear visual choice: Any additional violence involving them and their associates will move their entire group up the priority list for the organized-crime investigations that have been so successful in putting away some of the city’s most violent offenders in recent years, they are told. Or, if they want out of the lifestyle and into the city’s job-training programs, they can be moved to the top of the list for help.

“The message that we deliver is that we know who you are. We know who you hang out with. We know that your group has committed acts of violence, and we’re here today to offer you an opportunity to put the guns down,” explained NOPD Commander Frank Young, who heads the department’s anti-gang units. “We will help you if you let us. We will stop you if you don’t.”

The most compelling moment of the call-in, Young said, is when a mother who has lost a son to violence addresses the young men directly.

“When the mother of that murder victim speaks, it is so moving you can hear a pin drop. When she tells her story about her son being murdered, and her life after her son’s murder — it’s almost as if it happened yesterday,” Young said. “She’s telling the tale of how her son’s murder has absolutely ruined her and broken her heart for the rest of her life. When she speaks, it definitely has an impact on them.”

The concept is based on research that shows the most effective deterrent to crime is the perceived probability of being caught, and when the gang members are confronted with how much the police know about them, the results tend to be immediate, according to the same University of Cincinnati study, which focused on the 2013 fall in murders in New Orleans. During the 18 months between October 2012 and March 2014, NOPD held five such call-ins with 158 offenders from 54 gangs. (Nearly 60 of them actually signed up for job training services, though only 25 actually followed through with participation.) Meanwhile, major-gang unit investigations have produced well over 120 organized-crime indictments among New Orleans street gangs, none of which were refused or resulted in acquittals.

As a direct result of that pressure, in 2013, “the City of New Orleans experienced a statistically significant homicide rate decline above the average homicide rate change for the 14 highly comparable cities … a 23% homicide rate decline that was specific and unique to New Orleans,” the University of Cincinnati study states. The reduction was concentrated in gang-member-involved homicides, which fell a total of 30 percent during the study period. Non-GMI homicides (such as domestic cases or random acts by otherwise non-violent people) fell only 10 percent. Likewise, “homicides involving Black male victims between the ages of 20 and 29 years old experienced a statistically significant decline of 26.7 percent,” concluded the study. And the decline in homicides corresponded to a similar decrease in non-lethal gun violence the same year, the report states.

Young, who spent most of his 20-year career in major investigations, including stints with the FBI and the DEA, said their research matches his own observations about 2013 as a turning point. When the gang units he now leads were created, Young was still assigned to investigations in the Sixth District, where many of the most violent gangs were located, and he could see their work take immediate effect.

“The same people getting shot were the perpetrators. The same witnesses would then become suspects in other crimes. It was a very small number of people that were responsible for the majority of the crime,” Young said. “I got to watch as these big groups got indicted, and I was the guy that watched all these numbers spiral downward.”

In most years, the changes in homicides in New Orleans are similar to changes in overall violent crime and property crime, so researchers say that the increased scrutiny on the most violent offenders seems to be working. It also bears on the notion of violence as a disease, in the phrasing of former Health Commissioner Karen DeSalvo: the Group Violence Reduction Strategy and other enforcement efforts are the front end.

“She [DeSalvo] would say, if you have a patient coding on the table, you try to address the heart attack they’re having right now,” said West, in the mayor’s office. “You don’t talk to them about healthy diet and exercise. You have to address the emergency. But, at the same time, you have to start planning for all the sustainable changes to lifestyle.”

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But if the progress was so clear in 2013, why has it since leveled off? Why isn’t it continuing to pay dividends in 2014 and 2015, and why aren’t murders continuing to fall?

Those answers aren’t as easy to come by. Many officers would blame the decline in manpower, as a total of only 77 new officers joined the NOPD between 2011 and 2014, while more than 100 per year were leaving. The report, meanwhile, notes researchers’ struggles to change the NOPD mindset regarding gang-violence, and to think in larger terms of groups and criminal networks. Researchers had to constantly oversee police reporting that overlooked gang relationships, and notes that this may be a requirement to keeping the program effective.

But the factors contributing to the violence in New Orleans fundamentally make the city “the most challenging of contexts” for reducing crime, specifically because of its “extremely high murder rates, political and police corruption, and a local culture seemingly more tolerant of violence,” the report also notes. And police and city officials agree that law enforcement’s ability to prevent violence is limited — after its tactics and resources are improved, the underlying problems still persist. Even as violent offenders are arrested, the communities they leave behind still suffer from the same social maladies, with a new generation poised to inherit them.

“Children that grow up in a household with family violence themselves often end up perpetrators later in life,” West said. “The degree to which [violence] is communicable is in large part because it is a learned behavior. Then later in life, these children when faced with conflict behave in the way they have seen.”

Much of the long-term effort to correct the problems that allow violence to incubate has focused on the staggering unemployment rate for black men, pegged at 52 percent in a frequently-cited 2013 study by Loyola University of New Orleans. City Council members have been vocal in insisting on local hiring by developers, and the city has been focusing on one of the hardest groups to find employment for, those with criminal records of their own. The city’s re-entry strategy, as it is known, provides not only job training for ex-offenders, but also extensive support networks to ensure they are ready for the workforce. The city has primarily focused on connecting those job-seekers to major institutional employers, but they are available for small businesses as well.

More than 100 people have successfully completed that program, West noted. City agencies are frequently ready to hire them, either for traditional jobs or newer ones, such as the lot maintenance programs that began as blight-reduction strategies and expanded to create jobs.

Will this public-health approach finally prove to be the key to unlocking New Orleans’ decades-long struggle with violent crime, or is it simply the latest metaphor for an intractable issue?

Dr. Andre Perry, who has documented striking differences in life expectancies among different New Orleans ZIP codes, agreed that the multiplicity of factors that give rise to violence in a community do bear a resemblance to “some organic system working in concert.” A public-health approach, Perry said, has the benefit of a long-term focus on root causes of violence, rather than reducing it to a simple policing or jailing issue, which allows inequality to fester.

“If you give people low opportunities, low education, this is going to happen,” Perry said. “The real consequence of not providing just and equitable system is a violent system.”

Ultimately, Perry said, the success of the public-health approach will be measured less by what law enforcement does and more by what structural changes the city can create. Individual programs for job training or diploma acquisition, he said, are only a start.

“It’s needed, but it’s not sufficient,” Perry said. “In New Orleans, it’s a much deeper structural problem around employment. We need to further reduce the prison system. Education needs to continue to improve over a longer period of time. We need greater structural change in order to see the kind of reduction that will serve residents well.”

The city’s radical income disparity makes the problem even more difficult to address. The wealthy, Morrell said, can afford to buy an additional sense of security through private guards funded by taxing districts, allowing them to think they can wall themselves off from the problem. Meanwhile, the middle class — those who would be both adjacent to the crime and empowered enough to demand attention to it — no longer exists.

“We have a problem in this city with opportunity,” Morrell said. “There is no black middle class in New Orleans any more at all. You’re either affluent or you’re poor. That middle class that would be the cauldron of outrage has dwindled.”

Deborah Cotton, the journalist who was injured in a mass shooting on Mother’s Day 2013, said the many social-service programs in New Orleans are a crucial step. But they are so frequently mismanaged or even stolen from by the civic leaders in charge of them, Cotton said, that their failures become part of the city’s enduring trauma. Unlike the field of medicine — where treatments are governed by extensive federal regulation, testing and scientific research — programs to help the poor live and die at the whims of the people running them, with little oversight or consensus about which are effective.

“We as a community do not get outraged about that,” said Cotton, recuperating this month from her latest surgery related to the 2013 shooting. “My feeling is that if we do not make their suffering a priority, and push for our poor community to get the education and job training and various program resources — if we don’t push for those changes and draw a hard line in the sand around squandering the taxpayer dollar — then I feel like we are participating in our own denigration.”

Even if NOLA For Life is driven by a strong public-health philosophy, and its programs are those that are needed, the city has done a poor job of explaining that to the public, Cotton said. For most people — from the people on the street, to the middle class to even many members of the city’s political and policy-making elite — NOLA For Life still sounds like another empty branding exercise, its actual workings “shrouded in mystery,” Cotton said.

“No one can articulate what it is or how it works. There is no way to tell if it is effective or not,” Cotton said. “We don’t have a buy-in, and we don’t understand how it works. There isn’t a place that the average citizen knows that they can plug themselves in to help.”

The situation stands in contrast to the obvious solutions of rebuilding homes that presented themselves after the hurricane, Cotton said.

“After Katrina, people wanted to help. There were all of these opportunities to get involved. People felt useful, and that’s how we were able to get our city back,” Cotton said. “People don’t feel useful in how to address this crime issue.”

And until those long-term treatments begin to take root, the short-term gains — even when statistically significant — will never be enough to earn the city a clean bill of health.

New Orleans still has one of the highest murder rates in the city — despite the 2013 decline, Cotton said. “20 percent is just not sufficient.”