Pomona was one of a few areas in Southern California to see a major spike in killings in 2013.
Homicides in the city jumped from 17 to 29, a 70% increase.
Communities patrolled by the Riverside County Sheriff's Department also recorded a homicide increase of more than 40%.
Pomona recorded only 11 homicides in 2011, and 17 in 2012. Officials say the 2013 total of 29 is the highest since the 1990s.
"We cringe every time there is homicide," said Pomona Police Capt. Michael Olivieri, who joined the department a year after the city saw a record 44 homicides in 1989. "We are not pleased. It is not acceptable. We believe we're going to suppress it."
Two factors appear to be contributing to Pomona's problems: violence between young people from warring street gangs and a depleted police force.
According to the city, the number of sworn officers in the department has declined by about 50 since 2010 due to budget cuts.
Police attribute many of the homicides to rising gang violence in certain sections of the city.
The department has been struggling to come up with an effective strategy. Police gang task forces meet every other month to go over gang intelligence, Olivieri said, and plainclothes officers routinely sweep the streets to catch criminals in the act. On at least one occasion, he said, a suspect tried to carjack a plainclothes officer.
"There's a conflict out there," he said. "And we're addressing it."
Resident Larry Edwards said the violence was hard to miss.
"Down that way, one guy got shot in the middle of the street," Edwards said, looking down Angela Street. "And down the way, around the corner .…"
Edwards has owned a four-unit building in the neighborhood since 1977, and called the violence "cyclical." He recalled four shootings in the area in 2013, including a teenager killed in an alley 100 feet from his building.
He pointed to bullet holes in his building's wall. "There's a gunshot, there's a gunshot," he said. He walked to a nearby light pole and pointed again. "Gunshot."
The Riverside County Sheriff's Department — which covers 17 municipalities and nearly 1.4 million residents — is also struggling to understand why homicides are up.
Though final numbers won't be ready until next month, the agency reported 55 homicides within its jurisdiction between January and October of 2013. An analysis of coroner's records showed at least five other homicides in the remaining two months of the year. The 60 homicides would mark a 46% increase from the 41 killings the department reported in 2012, and the most the agency has seen in the last five years.
As in Pomona, officials in Riverside are puzzled at why there are more killings when preliminary figures show overall violent crime is down.
"We sat down and tried to brainstorm and come up with any trends and see an increase in one particular area, and we didn't come up with anything," sheriff's Lt. Lisa McConnell said. "It's all scattered."
The department's full-time homicide unit has closed more cases in the last year, McConnell said, reporting a 65% closure rate for 2013 homicides compared with 59% the year before.
"It's not a matter of they're just looking at the numbers," McConnell said. "What can we do differently? Are we missing something? They're constantly reviewing their cases and trying to figure it out."