A state government report said on Friday that California's homicide rate fell by 7.8 percent in 2010 to the lowest level since 1966, in-line with a U.S. drop in violent crimes that researchers have attributed in part to better police work.
The nation's most populous state had a homicide rate of 4.7 per 100,000 population, down from the year before when the rate was 5.1, said the California Department of Justice.
In another significant development, the homicide rate from 2001 to 2010 fell by a quarter, the agency said.
The decline in the number of killings in major California cities such as Los Angeles, where drug and gang violence decimated neighborhoods in the 1980s, comes as the nationwide murder rate has also been falling.
A report from the FBI said an estimated 14,748 people were murdered in the United States in 2010, which was a 4.2 percent decline from the year prior and an 8 percent drop from 2001.
Social science researchers have given many reasons for the years-long fall in murders and violent crime, but many admit to being baffled.
"It's a riddle," said George Tita, a professor of criminology, law, society and planning at the University of California, Irvine.
"A lot of our social science theories would predict that when the economy is bad and increasing the level of strain and frustration among people, that it's more likely to lead to violence," Tita said.
But the opposite has happened, as reachers note that violent crimes rates decreased in the United States even as the country struggled with a recession, and then a sluggish economic recovery.
A spokeswoman for the California Department of Justice said the agency could not provide reasons for the drop in homicides to the lowest level since 1966.
A main factor appears to be smarter policing and better law enforcement tactics, Tita said. Police chiefs are "more efficient in allocating resources to problem areas" by using data and technology, he said.
Mark Kleiman, professor of public policy at the University of California, Los Angeles, said the period from 1965 to 1994 saw an unusually high amount of crimes.
"One way to think of it is we're getting back closer to historical norms," he said. "... The crack (cocaine) epidemic has largely burned itself out."
Researchers also point to the high rate of incarceration as a reason for the decline.
California has about 150,000 people in custody, and it has placed so many convicts behind bars that the U.S. Supreme Court in May ordered state officials to release inmates and take other steps, because of overcrowding in prisons.
Thousands of state inmates are being transferred to county jails to reduce pressure on the clogged prison system.
The California Department of Justice report on homicides said that in 2010, 80 percent of those killed by homicide were men and boys.
The breakdown along racial lines of murder victims provided by the state agency compared to population data from the 2010 U.S. census suggests that African-Americans in California are far more likely to be murder victims than whites.
Only 18 percent of California victims were white compared with 40 percent of the population, while 30 percent of victims were black compared with only six percent of the population. Hispanics accounted for 45 percent of homicides compared with 38 percent of the population.
The vast majority of the state's homicides involved guns, and among those killings in which investigators uncovered the contributing circumstances, 36 percent were gang related, the report said.
The Department of Justice said its 2010 homicide figures are the most recent available.