Homicides and thefts are on the rise in Roanoke compared with the first half of last year, while the number of other violent crimes, burglaries and vehicle thefts are down, according to data from the Roanoke Police Department.

The increases reflect a national trend, but explanations about why it is happening in Roanoke differ.

Criminologists say crime rates across the nation are rising because of the slumping economy. But police in Roanoke believe the economy has played only a small role in the increases here. They said that most crimes they investigate are drug-related, and that the perpetrator and victim typically know each other.

They haven't been able to explain the increase in homicides because there is no pattern to the deaths, police said.

The number of homicides can fluctuate drastically from year to year in the city, which had eight homicides in the first half of 2008, compared with just one last year in the same period. By the end of 2007, there had been just four homicides -- a low that has been reached just one other time in at least 40 years. In 2006 there were 11 homicides, and 16 the year before that.

"You're going to have good years, and you're going to have bad years," said Roanoke police Capt. Chris Perkins.

Police have placed charges in six of the eight homicides this year. The other two were murder-suicides.

Despite their success at making arrests in this year's homicides, detectives are having a more difficult time getting information because of a lack of cooperation from witnesses or families, Perkins said.

"When someone dies, someone needs to come forward," he said. "It is a shame we've gotten to a point in our society to let someone die and keep your mouth shut."

The "Stop Snitchin' " movement, used by criminals to scare people from reporting information about crimes, has become widespread, Perkins said.

Police also believe that witnesses won't talk because they don't want to be associated with other crimes that may surround a homicide, such as the use or sale of drugs.

"We have a drug problem [in the city] and it is fueling a lot of things," Perkins said.

Police said that drugs are partly responsible for the 15 percent increase compared with the midpoint of last year in larcenies, such as shoplifting or stealing items from cars, that Roanoke has seen in the first half of 2008. They believe some people steal so they can get money to sustain their drug habit.

The number of larcenies decreased 20 percent from 2004 to 2007. But the increase in the first half of this year has put it on track to exceed last year's total. Of the larcenies reported in the past six months, 48 percent happened at stores or from vehicles.

Roanoke County also has seen an increase in larcenies, which were up 8 percent the first half of this year compared with last year, according to data from county police.

County Police Chief Ray Lavinder said he did not want to speculate about reasons for the increase.

But experts believe the economy is behind the rising number of thefts nationwide.

"The economy is in a sour mood, and we should expect crime rates to increase," said Richard Rosenfeld, a University of Missouri-St. Louis criminologist who has studied how the economy affects crime.

Most of the larcenies in the country are reported as thefts from stores. Grocery stores are becoming a popular target, Rosenfeld said.

Where Roanoke is bucking the national trend, Rosenfeld said, is in its decrease in robberies, which involve the use of violence or threats, and burglaries, the entering of a building unlawfully intending to commit a crime.

Though robberies rose 35 percent from 2004 to 2007 in Roanoke, the number is on track to decrease this year. There have already been 51 fewer robberies the first half of this year than last year.

Roanoke police attribute that drop in robberies, and a 14 percent decrease in burglaries from last year, in part to education.

"It is important people help themselves not be a victim of crime," Jennifer McKeldin, the department's crime analyst.

The department has been promoting its "Lock It or Lose It" campaign, and in anticipation of an increase in robberies in the summer, police this spring talked with business owners in areas that have a history of problems.

Officers also are increasing their visibility by patrolling those areas more frequently, and even parking near businesses while they do paperwork.

But police can only do so much.

Too many people believe that it is OK to leave their cars or homes unlocked because they are in a "safe" area, McKeldin said.

"It is not about where you live," she said.

"For some reason, people feel like its never going to happen to them, but it does."