Metropolitan Tucson has gone more than a month and a half without a homicide, a welcome break in an area that normally sees a slaying a week.

Police and sheriff's detectives agree it's an unusual trend and say it's allowing them to get in some work on some unsolved cases.

Four men have been killed in Tucson and Pima County since the beginning of the year. Arrests have been made in three of the cases. Those homicides happened in the first two weeks of the year and were scattered across the metro area: one each on the South Side, the East Side and the North Side and in the Green Valley area.

Unfortunately, it's hard to know what's caused the low numbers in the first two months of this year, said Gail Leland, director of Homicide Survivors, a local support group. If officials did know, they'd also know what to do to prevent homicides in the future, she said.

Homicide Sgt. Kevin Hall of the Tucson Police Department said he doesn't speculate on why there have been no new murder cases.

TPD homicide detectives have been using the break to investigate unsolved cases from a "horrible" rash of homicides in October and November, he said.

There were 31 homicide cases in the city and the county between Oct. 1 and the end of the year, accounting for 35 percent of last year's homicides.

"They've been able to do some pretty significant work on older cases," Hall said.

Three or four cases are ready to be presented to the Pima County Attorney's Office, and prosecutors will decide whether to seek indictments. Hall said detectives hope to make arrests in those cases within about a month.

Homicide detectives don't rest when new cases are few, said homicide Sgt. Brad Foust, of the Pima County Sheriff's Department. They work on follow-ups requested by prosecutors, or attend trials and help investigate other types of cases that involve victims with life-threatening injuries, such as shootings.

City and county homicide detectives handle 10 or more cases apiece each year. The city's homicide unit currently has five experienced homicide detectives, a new homicide detective and a new cold-case detective. The county unit has seven homicide detectives and two cold-case detectives.

Criminologists would not be wise to make much of a six-week homicide-free trend, said Robert Friedmann, director of the Improving Crime Data project at Georgia State University in Atlanta. Homicide numbers fluctuate with the season, the time of day, the level of drug gang warfare in an area and other factors, he said.

Friedmann's project ranks 67 U.S. cities based on homicide rates and then ranks them again after adjusting the figures for demographic and social differences, such as poverty and unemployment levels and population turnover, he said.

Tucson rises from number 34 to number 26 when its figures are adjusted, Friedmann said. That shows the homicide rate in Tucson is higher than expected for a city with its set of characteristics, he said, placing it alongside cities such as Boston and Newark, N.J. San Francisco ranked highest.

Tucson's homicide rate consistently hovers around 10 homicides per 100,000 people, according to Tucson Police Department data.

On StarNet: Want to know more about crime in Tucson than can fit in

the pages of the Star? Check out the StarNet Police Beat blog at

azstarnet.com/crime