Crime is dropping throughout much of the country, but statistics show that one category of violence is bucking the trend: murder.Some of the nation's largest cities-New York, Chicago, Los Angeles and Philadelphia-are reporting slight increases in murders so far this year, according department records. That's due in part to shootings involving multiple victims and unexpected spikes in domestic killings, criminal justice analysts say.

"What I've seen in several places is a period of volatility that we haven't seen for a while," says Chuck Wexler, executive director of the Police Research Forum, a law enforcement think tank that tracks violent crime.

Although crime has been driven to record lows in some areas of the nation, Rob Davis, president of the Major Cities Chiefs Association, says there is no evidence that it has "bottomed-out."

"We will always see spikes," Davis says. "I think it is hard to draw long-term conclusions."

Among the cities where murder is up through the first four months:

New York. The city has recorded 149 murders, up from 134 at the same time last year. Included in this year's running total is 13 domestic killings involving victims 9 years or younger, police spokesman Paul Browne says.

Browne suggests that the city, which for years has seen steep drops in crime, may be a victim of its own success. The first four months of last year marked the lowest first-quarter murder numbers ever recorded, Browne says.

Chicago. A spasm of violence last month, in which five family members were slain in a domestic shooting, helped push first-quarter murders to 120, up from 111 at the same time last year.

In all, 11% of the 2010 murders are domestic killings, Chicago Police Superintendent Jody Weis said, adding that other major violent crimes (robbery, sexual assault and aggravated assault) were down by 13%. "We cannot ignore the destructive nature of guns and how their presence can escalate a volatile situation into a tragic one," Weis said.

Los Angeles. Although overall violent crime is down 13% so far this year, murder is slightly higher, up from 100 last year to 103 this year.

It is the only major crime not in decline, according to police crime statistics.

One dramatic violent incident, Police Commander David Doan says, represents the difference in the higher murder number. Last month, a gunman opened fire in a San Fernando Valley restaurant on a Saturday afternoon, killing four people.

"We pay very close attention to the trend lines," Doan says. "We believe we're (moving) in the right direction. The challenge will be in the warmer months" when crime tends to increase.

Philadelphia. The slaying of a 68-year-old handyman earlier this week is one of the reasons why murder is up slightly, from 101 last year to 104 so far this year, Police Lt. Frank Vanore says.

Overall violent crime is down 8% in Philadelphia - but Vanore says there are still "absurd" cases of violence. "There is no rhyme or reason," he said.