Major violent crimes in Aurora increased across the board in 2015, with homicides rising by a whopping 118 percent, according to numbers released by the Aurora Police Department.

At the same time, the number of arrests and cases in which summonses were issued declined, baffling city officials as to why crime is up but arrests are down.

“There’s concern, but there doesn’t seem to be any logical reason why,” said Aurora City Councilwoman Barb Cleland, chairwoman of the city’s public safety committee. “Most crimes are going up.”

In 2015, there were 24 murders committed in the city, compared with 11 the previous year. However, 2013 saw 23 homicides, and in 2012, there were 29, but that year includes the Aurora theater shooting, when 12 people were killed.

As for arrests, Aurora recorded 10,975 last year, compared with 11,655 in 2014.

Traffic enforcement numbers also were down in four of five categories, and drunken-driving arrests were down 10 percent compared with the prior year.

Aurora has a homicide rate of 6.2 per 100,000 residents — compared with Denver at 7.5 and Colorado Springs at 5.8 — based on 2014 U.S. Census Bureau population figures. Aurora has about 353,000 residents, according to the latest estimates, and has grown by about 30,000 people since 2010.

Nick Metz, who started as the city’s police chief in March 2015, is off this week and was unavailable to comment.

But Deputy Police Chief Paul O’Keefe said the 2015 homicide numbers are closer to the 10-year annual average of 23 homicides in the city. He said the 11 homicides in 2014 marked “a good year.”

The last time Aurora saw 11 homicides, O’Keefe noted, was in 1999, adding that “2015 is back to average” for Aurora.

“One is too many, but it’s unrealistic to think we’re not going to get through a year without any homicides,” O’Keefe said.

He said homicides also are trending upward in other cities throughout the country.

Denver, for example, recorded 50 homicides in 2015, up from 31 the previous year.

Police Sgt. Bob Wesner, president of the Aurora Police Association union, doesn’t agree with the “average” reason. Wesner said the department is woefully understaffed, preventing it from doing community outreach to deter criminal activity.

The Aurora Police Department, which has 660 officers, should be at 682, Wesner said. Even after the current police academy cadets graduate and are trained, Aurora won’t reach its targeted staffing levels until 2017, he said. Retirements and officers leaving for other departments also have been factors.

“Our policing has changed in the way we respond to calls for service, and they have very little time to do proactive law enforcement,” Wesner said. “They don’t have the time to do the proactive stuff and bring the crime rate down.”

O’Keefe said more patrol officers were added in 2016, and the SWAT team was beefed up, as well.

Aside from homicides, the number of sex assaults climbed from 300 in 2014 to 385 last year, an increase of 28 percent, according to the police department.

O’Keefe said part of that rise is the result of victims being more willing to report sex crimes now than five or 10 years ago.

Robberies and aggravated assaults also increased — by nearly 7 percent and 11 percent, respectively.

Overall, major violent crimes rose by 14 percent in 2015.

In memos to Metz, several top police officials cited other possible reasons besides staffing and blips on the radar screen. Those included the city’s population growth, increased calls for service, construction of light rail pushing crime into other areas and the impact of legalized marijuana on the underground pot trade.

“If anything, the trend recently has been a significant increase in the amount of robberies, assaults, aggravated assaults as well as murders that have come to fruition as a result of face-to-face marijuana deals that have ‘gone bad,’ ” wrote Capt. Christian Lertch of District 1 in north Aurora.

The Rev. Gene Roncone of Highpoint Church in Aurora has served on a city committee that addresses gang issues. He said more gang members are moving east from Denver — and crime is moving with them.

“Most of those violent crimes come from the urban corridor, and they have spread south,” Roncone said. “That’s part of the urbanization of the city.”

On a positive note, O’Keefe noted that burglaries were down by nearly 14 percent in 2015.

In a city that calls itself Colorado’s safest large city, officials say public safety needs to be a greater priority than it is now.

“My personal opinion is that we have to make more of an effort,” Cleland said. “As far as funding, that’s something the council will have to deal with in our next year’s budget. We’re going to have to look at it and see where we are and see how many police officers we have to add.”

Carlos Illescas: 303-954-1175, cillescas@denverpost.com or @cillescasdp