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Violent crime is up across the U.S., and top cops from America’s biggest cities met in D.C. Monday to talk about it.

After hours of discussion at the Newseum, the Major Cities Chiefs Association—an organization of police executives from the country’s largest cities—held a conference at which the group’s president, Thomas Manger, presented recommendations for beating back homicides and armed assaults. Manger, who is also the police chief of Montgomery County, said law-enforcement staff need to build community trust through “accountability and transparency,” while policymakers must find effective ways to address larger social problems such as mental illness, unemployment, and lack of access to education. Still, Manger and other officials who spoke at the event, including D.C. police Chief Cathy Lanier and St. Louis Mayor Francis Slay, admitted policing alone can’t solve the growing violent-crime problem in the U.S.

“What we’re dealing with here is bigger than any one city,” Manger said. He later added that “there’s no clear answer” for why violent crime has jumped nationwide so quickly this summer.

Manger shared statistics from an MCCA survey of 35 cities: in the past year, nearly two-thirds of them saw more homicides; two-fifths reported a greater number of multiple-firearm shootings; half experienced increased gang and retaliatory violence; and almost one-third had more incidents of violent crime where the offender was under the influence of synthetic drugs—a hot topic in D.C.

Asked whether synthetic drugs were a “red herring” for the uptick in violent crime, as DC Police Union Treasurer Gregg Pemberton put it in a blog post last week, Lanier responded, “no one in our discussions said that was the primary problem,” though synthetic drugs appear to be a factor. “Consistently we have seen that drugs historically have been and always will be a part of the violent-crime cycle, because people are going to compete for territory and that brings violence,” she said.

There have been 87 homicides in the District this year. Fewer than half of them have been closed with arrests, according to WJLA. These represent roughly a 20 percent uptick over 2014.

Among the recommendations Manger introduced at the conference were strengthening prisoner reentry programs to reduce the number of repeat offenders, improving testing for synthetic drugs, and creating harsher penalties for people who commit violence with high-capacity guns. Manger also called for the U.S. Department of Justice to build a national database of crime information that would allow local jurisdictions to capture and share crime stats.

“We don’t know what’s going on in real-time in other cities like ours around the nation,” he said.

Photo by Andrew Giambrone

Correction: This article originally misstated the share of cities surveyed by the MCCA which indicated they saw more homicides in the past year: It was nearly two-thirds, not a quarter. We regret the error.