Oklahoma City concludes 2012 with a grim record: the second highest number of homicides ever recorded in Oklahoma's largest city.

As of Monday, 99 people had been killed by another person in the city during the year, according to police records. Gang-related homicides doubled compared to the previous year, and sharp increases were also seen in justifiable homicides, such as self-defense.

The total is the most since 102 homicides were reported in 1979, though the ranking does not include 1995, when the bombing at the downtown federal building killed 168 people. The city recorded 60 homicides in both 2010 and 2011.

Police officials noted the spike in homicides compared to previous years, saying it wasn't clear what may have led to the sharp increase. But police Chief Bill Citty said "in most cases, there is some kind of drug nexus."

"There's nothing that points to the economy. We really don't know why it jumps up or goes down from one year to the next," added Sgt. Gary Knight, though he said gang activity, illegal drug trafficking and domestic violence are leading factors in homicide cases.

Citty noted that the city's aggravated assault rate has been creeping up in recent years. "As that goes up, your homicide rate is bound to go up," he said.

Gang-related homicides rose to 28 from 14 last year, and there were 11 robbery-related homicides compared to just one last year, Citty said.

Deaths resulting from officer-involved shootings increased to six compared to two in 2011, and there were 10 self-defense-related homicides — compared to none in 2011. Both are included in homicide statistics as justifiable homicides.

Citty said 71 percent of the city's homicides involved firearms.

City manager Jim Couch didn't cite any specific steps police or the city could take. But he said that when faced with such statistics, city leaders must consider issues such as increasing the number of police officers who patrol the streets and the social services available for people experiencing personal difficulties.

There were about 1,000 police officers in the city at the end of November, though the city's budget authorizes a total of 1,058 officers.

"No homicides are acceptable, but you're going to have them," Couch said. He also said that when individuals join gangs or deal drugs, "your risk is often times associated with life choices."

Knight said Oklahoma City recorded 191 drive-by shootings in 2012, which contributed to the number of deaths investigated by the police department's 14-member homicide unit.

"It's more cases than they've handled for some time. But they are professionals. They are at the top of their field," Knight said.

By comparison, Tulsa — Oklahoma's second largest city — had recorded 46 homicides in 2012 as of Monday, Tulsa police Sgt. Leland Ashley said. The most homicides ever recorded in the city was 71 in 2009, Ashley said.

Oklahoma City has about 580,000 residents, while Tulsa about 390,000, according to the 2010 census.

As in Oklahoma City, Ashley said most of Tulsa's homicides occur between people who know each other.

"We do not have a lot of stranger homicides. Somehow, they know each other," Ashley said.