Crime in Los Angeles County is at record lows - but the gains are uneven and there are many theories as to the reasons.
"This crime drop is not experienced equally by everyone," said UC-Irvine Criminologist Charis Kubrin, who says crime is better examined on a neighborhood level.
Compton, for instance, saw 10 more homicides than last year, as of the Nov. 2012, the latest available figures. LAPD's Southwest station saw nine more homicides reported this year than last in its dataset, which runs through Dec. 21. And some historically tough areas, like Southeast L.A., saw homicide remain relatively high and steady.
Overall, homicide rates across the nation have plunged, declining by nearly half in two decades.
"This is one of the longest crime drops we've seen in some time," Kubrin said. Explaining the cause happened is not so easy.
"Crime rates in L.A. and elsewhere are comprised of so many different factors," Kubrin said. "There's realignment, and our incarceration policies - those things play a role. So do things like poverty, inequality, the housing market, foreclosures, all of that."
Popular theories abound on what's behind the U.S. and L.A.'s crime drop. Here are five of the most-often cited ones:
Crime spiked in the 1980s, during the now-infamous "crack epidemic" of that decade. As the world moved on, crime came back down.
"The drop in the 90s was driven by aggressive policing and the fading of the crack market," Pepperdine University Criminologist Alfred Blumstein told NPR member station KQED. "The question is what's happening now."
Skipp Townsend, one of the leaders of the Southern California Ceasefire Committee and executive director of the violence reduction program 2nd Call, said crack isn't the best explanation.
"Drugs are still prevalent in the community, " he said. "What took over from crack is now meth. Drugs are always going to be prevalent in society, period."
At the same time crime rates dropped in the U.S., the incarceration rate has spiked. In 1980, before the prison boom, there were 474,368 people in jail or prison in the United States. By 2012, that number was more than 2.2 million.
Many have suggested the two are related.
Criminologists generally say there are three things prison could be used for: deterrence, rehabilitation, and incapacitation - taking people out of communities so they won't be committing crimes in those communities.
In 2008, Pew interviewed Blumstein and criminologist James Wilson (famous for authoring the "broken windows" strategy). The two said rehabilitation in prison has not been a priority for decades. The deterrent effect of imprisonment has some value, they said, though they questioned whether sentences need to be as long as they currently are to have a deterrent effect.
Incapacitation, they said, is probably prison's greatest value.
They cited studies concluding the use of prison accounted for about 25 percent of the crime drop during the 1990s.
But UC-Berkeley Criminologist Franklin Zimring wrote about New York City, where crime continued to drop in the 2000s even as the state's prison population dipped. In California, juvenile crime has continued to drop even after the state massively downscaled its juvenile prison system over the past six years and youth arrests dropped.
As Zimring studied New York City's crime drop, he found the size of the police force and quality of policing changed dramatically during that period. Police have gotten better at solving crimes and even preventing crimes, he said.
In L.A., police have been building better relationships with the communities they serve. Cops are also embracing social science — using crime data and mapping to chart out hotspots and target their resources. A relationship with the community helps police solve crimes, and statistics help police decide where to deploy a visible presence. The theory is both factors deter future crimes.
Major police departments now keep crime analysts on staff. At LAPD, station captains are tethered to their phones and iPads, which constantly update them on crime trends, allowing them to rapidly respond to upticks in a particular area with extra patrols.
There's also been a rise in community groups focused on lowering crime, Townsend said, like gang interventionists, mediators, and anti-violence programs.
"I think what's happening now is the community is talking to each other," he said. "We don't just accept the violence as part of the dysfunction that comes in the community."
"One of the biggest correlates for declining crime rates, not just in Los Angeles, is increases in immigration to large cities," said Kubrin, who's seen that connection emerge in her own research.
Others have seen the same effect in Brooklyn, San Diego, and Houston.
"It's not the only reason crime has declined, but it's part of it," Kubrin said.
Another demographic factor to look at, according to UC-Berkeley Criminologist Barry Krisberg, is the upbringing of people who are now young adults.
"Crime in primarily committed by people in their 20s," says Krisberg. That group now, is "the Clinton babies," Krisberg says.
"This is a generation that grew up at a time when unemployment rates were incredibly low and there was lots of federal investment in programs for young kids," Krisberg says.
Lead has become something of a boutique explanation for the crime decline, but one that's seen a growing following.
The theory, outlined extensively in a piece in Mother Jones earlier this year, is that childhood exposure to lead in gasoline during the 1980s caused criminal behavior when those children became adults. As a result, when new standards pushed down the lead content in gas, crime declined.
Krisberg said "there's no conclusive research" on the theory.