The Austin Police Department is facing its fifth spike in the number of murders committed during the past 15 years — despite an overall drop in the violent crime rate.

Murder rates usually average in the low to mid-20s every year, and 2007 marked the latest rate increase, said APD Cmdr. Julie O’Brien, who oversees the violent crimes division. But since January 2010, police have reported 31 homicide victims, 14 more than the same time last year.

O’Brien said although several homicides happened in unusual ways this year — such as the death resulting from Austin resident Joe Stack flying his plane into the Echelon Building on Feb. 18 — family violence and altercation-type murders were the most prevalent in 2010.

“Austin remains one of the safest cities for its size in the country,” O’Brien said. “Even with the increase in murders, we have been diligent in looking at all cases to inform us what kind of information we should be sharing with our partners about how murders can be prevented.”

Police have not found any commonalities among the homicides, and O’Brien said the murders occurred throughout the city. Authorities do not know the cause for the increase, but demographic, economic and cultural shifts could account for the higher murder rate, said Michelle Richter, an assistant criminology professor at St. Edward’s University.

“There have been some economic stresses within the community,” Richter said. “We are entering the period around the holidays when coping mechanisms may be stressed. The addition of alcohol, money anxiety and stress of family pressures may result in violence.”

Richter said she expects more murders to occur before the end of the year because of additional holiday stress.

According to police statistics, 67 percent of the victims were related or acquainted prior to the incident, and the most common weapon used is a firearm. Richter said it is difficult to determine what types of guns suspects use to commit homicide, since it depends on their preference and availability.

While accessibility of weapons and alcohol consumption may contribute to homicides, murders are also affected by factors individuals cannot control, Richter said. The public, however, continues to fear being the next victim, she said.

“Public perception and concern often fuel demands for legislative action and legislative reforms,” Richter said. “The fact is that the national murder rate is about 5.5 people per 100,000. In 2009, Austin was at 2.9, which is very low.”

Of the 31 murder cases in 2010, APD solved 27 of them — or 87 percent — surpassing the 2009 national average of 66.6 percent.

Public Safety Commission Chairman Michael Lauderdale said the agency asked APD to compile data of the murder rates and features over the last 10 years to analyze possible causes of the increase and preliminary changes to the city and department.

“We may have a statistical variation, and no particular thing accounts for that,” Lauderdale said. “If we can start to say it is a true increase, we can start to identify the characteristics and how we might deploy our resources.”