NEW YORK - Gangs, drugs, easy access to guns and a disturbing tendency among young people to pull guns to demand respect were among the causes authorities cited in trying to explain this year's increase in murders in New York and many other major cities after years of decline.
The number of murders reached its highest levels in a decade or more in some places, but some big cities, including Los Angeles, reported drops in the number of murders.
New York reported 579 homicides through Dec. 24 - a nearly 10 percent increase from the year before. The spike mostly reflects an unusually large number of "reclassified homicides," or those involving victims who were shot or stabbed years ago but did not die until this year. Thirty-five such deaths have been added to this year's toll, compared with an annual average of about a dozen.
At the same time, Police Department spokesman Paul Browne noted that this year's total comes after last year's 539 homicides - the city's lowest death toll in more than 40 years.
Browne blamed the rise in part on the availability of guns, particularly weapons from out of state. The city this year sued dozens of out-of-state gun shops that it says are responsible for many of the illegal weapons on the city's streets.
In Chicago, homicides through the first 11 months of the year were up 3.3 percent compared with the same period in 2005, reversing a four-year decline.
Houston police attribute a 15 percent increase in the homicide count to the influx of Katrina evacuees from the Gulf Coast.
"So we expect that to settle," Lt. Murray Smith said. "We're hoping it will go down."
Some cities, such as Cincinnati - which has had 83 homicides so far, up from 79 in 2005 - posted their highest numbers ever. Others saw their highest death tolls in years.
Oakland, Calif., had 148 homicides as of Wednesday, up 57 percent from last year. The number was the highest in more than a decade.
Philadelphia's 2006 homicide total was 403 as of Wednesday, the first time the number has topped 400 in nearly a decade. There were 380 murders in 2005.
Philadelphia officials have struggled all year to reduce the violence. In July, Mayor John F. Street gave a televised address in which he pleaded with young people: "Lay down your weapons. Do it now. Choose education over violence."
In New Haven, Conn., homicides were up this year by more than 50 percent, to 23 as of Tuesday. Police chief Francisco Ortiz said young people were too quick to use firearms.
"They're all struggling with this thing about respect and pride," he said. "It's about respect. It's about revenge. It's about having a reputation. It's about turf, and it's about girls."
Los Angeles' total was down about 4 percent to 464 homicides through Dec. 23. San Francisco's fell about 15 percent. San Francisco Police Sgt. Steve Mannina said the drop is partly due to increased patrols in violence-prone areas and the approval of more overtime.
New Orleans, with its post-Katrina exodus, is the only major U.S. city that saw a sharp decline in the number of homicides. Police spokesman Sgt. Jeffrey Johnson said there were 154 in New Orleans this year as of Monday, down from 210 in 2005. But the city was largely empty during the fall and winter of 2005-06, and even now has only about half of its pre-Katrina population of 455,000.
The FBI does not release its national crime statistics until several months after the end of the year. The bureau's statistics for the first six months of 2006 showed an increase of 1.4 percent in the number of murders in the first half of 2006 compared with the same period in 2005.
Andrew Karmen, a criminologist at John Jay College in New York, said that while there are various theories for the drop in murders in New York and other cities in the 1990s, no one knows for sure why they decreased. He noted that police departments tend to take credit when the murder toll goes down.
"When crime goes up, it will be interesting to see whether they will accept responsibility," Karmen said.