D.C. Police Chief Cathy L. Lanier, right, and Mayor Muriel E. Bowser hold a news conference May 15 on the murders of four people in the District. (Bill O'Leary/The Washington Post)

More than 10 percent of the District’s spiking number of homicides this year have involved previously known violent offenders who have recently been released from prison, D.C. Police Chief Cathy L. Lanier said Thursday.

“Multiple of our offenders involved in homicide have previous homicide charges and are recently back in the community,” Lanier said at a news conference.

Lanier said that police so far have identified 10 such people, out of the city’s 91 homicide cases this year. “Ten. That’s significant and it’s different from anything we’ve seen before,” she said.

D.C. police declined to name the people who Lanier was referring to . Gwendolyn Crump, a police spokesperson, later said that the 10 people Lanier was referring to included victims.

Lanier, who addressed reporters alongside Mayor Muriel E. Bowser, following a meeting between the District’s top safety officials, said Thursday that she still did not know what was driving the city’s rising homicide count, which hit 91 this week — a 28 percent increase from this time last year.

Mayor Muriel E. Bowser said that she still did not know what was driving the city’s rising homicide count, which hit 91 this week — a 28 percent increase from this time last year. (WUSA9)

Nearly four people have been killed, on average, every week in the District since June 1 alone, and city officials are under pressure to show that they are undertaking a meaningful strategy to stem the tide.

District police have responded to the murders by fanning out in some neighborhoods — as in Woodland Terrace in Southeast Washington, which has seen a tenfold increase in police — and by altering their patrols and visibility in other neighborhoods, Lanier said.

But the slayings have continued, sometimes in the course of petty arguments.

“In some of the violence we’ve seen recently, it has just been dispute resolution with a gun. It’s that simple,” said Lanier.

Bowser (D) said officials met Thursday to discuss crime statistics, trends and tactics. But it was unclear if the meeting had produced any new strategy. Following the meeting, she told reporters that the police chief was continuing to review deployment strategies and that officials were considering “preventive measures” such as better lighting and cameras in public housing and high crime areas.

Bowser also said her team is examining potential legislative changes that could facilitate police efforts—and that they are focused on making sure the existing system for arresting and prosecuting violent criminals is working “as it should.”

She noted the recent appointment of a new director of the city’s Department of Forensic Sciences, and said that she and other city officials have asked the agency to process evidence more quickly “as it relates to homicides.”

Fifty-five of the District’s 91 homicides so far this year are still open cases, according to Crump.

Defending the number of unsolved cases, Lanier pointed Thursday to the challenges of solving most homicides, which she said often take place in “isolated” areas with poor lighting, no cameras and no known witnesses.

DNA, fingerprints and firearm analysis also take time, she added. “So a lot of times we have a suspect identified very quickly but to bring the actual arrest takes more time,” Lanier said.

Bowser and Lanier addressed reporters on Thursday beside a display of six homicide suspects and victims, including two recently closed cases, urging local residents to help police identify suspects.

“Most of the posters in front of me show victims, and we need the community’s help to find who is responsible,” Bowser said, identifying the men on the posters by name. “Shawn Simmons’s killer is at large,” she said, referring to one man who was shot in Southeast Washington on Aug. 1.

The District offers a reward of up to $25,000 for information leading to the arrest and conviction of a homicide suspect. Bowser urged D.C. residents to make use of the city’s anonymous tip text message service at 504-11. “If you see something, even if you think it’s insignificant, it may be helpful to our investigators,” she said.

Earlier this month, Lanier hosted a summit for police officers from other cities across the nation. She said that homicide rates are spiking elsewhere, and that police forces are finding more guns, and more high-capacity magazines on city streets.

“Every city is seeing a flood of these high-capacity magazines,” she said Thursday. High-capacity magazines allow shooters to fire more rounds than they might otherwise, making altercations more lethal.

District police are finding crime scenes “where there are 40 to 50 rounds fired,” Lanier said.

Lanier speculated that changes in gun laws across the country in recent years have contributed to the influx that the District — which has some of the toughest gun control laws in the nation — and other cities are now seeing. She noted that consumers have purchased high-capacity magazines in other states, fearing that they would soon be banned.

“And is it possible that maybe some of those are now making their way to major cities? We don’t know. But for some reason, they are showing up in every city,” Lanier said.