Violent crime has spiked in a number of large American cities, including New York, Chicago and Houston, with Baltimore seeing one of the steepest increases in homicides.
A common reason for the simultaneous rise in violence across disparate landscapes is difficult to pinpoint. Criminologists and public officials point to a range of possible factors, including easy access to guns, drug battles and failure to address underlying issues such as poverty and addiction.
Some also speculate about a so-called Freddie Gray effect or Ferguson effect, in which police are hesitant to do their jobs and criminals are emboldened to resist authority.
Charis E. Kubrin, a professor of criminology at University of California at Irvine, said cases of alleged police brutality around the country could be causing ripple effects. Incidents captured on video can compound the tensions.
"It's legitimacy. If you don't buy into the system, you don't participate," she said. "You want people to follow the rules — if you don't believe in that system, you just aren't going to do that. Right now, we are at a moment where the legitimacy of this system is being questioned in a major way."
Police chiefs and mayors from across the country addressed the national trend in separate discussions this week, with interim Police Commissioner Kevin Davis joining other law enforcement leaders in Washington and Mayor Stephanie Rawlings-Blake's top staffers participating in a conference call with the U.S. Conference of Mayors.
Civil rights leaders are also weighing in, with the Rev. Jesse Jackson calling for a deeper investment in urban areas to rebuild neighborhoods.
Rawlings-Blake will convene a meeting of American mayors in Baltimore in October to talk about how to resolve the issues that confront cities, said her spokesman, Kevin Harris. The group will develop strategies for combating violence, addressing poverty and providing access to jobs and health care.
"It's not just the spike in violence that concerns the other mayors; it's the volatility of the communities," Rawlings-Blake said in an interview. "When Baltimore erupted in violent protest, they understand very clearly it could happen anywhere. The mayors around the country, in many of the big cities that are experiencing spikes in homicide, we're all looking at each other for ways we can combat that issue."
The mayor, prosecutors and law enforcement officials created an around-the-clock "war room" this summer in response to the violence. This week, police announced that 10 federal agents would temporarily join the city Police Department's homicide unit.
The Major Cities Chiefs Association, an association of police officials, estimates that homicides in large cities are up 19 percent on average from this time last year.
A rising number of homicides have been recorded this year in cities as different as Chicago (up 18 percent from last year), Milwaukee (up 117 percent), Houston (up 36 percent), New Orleans (up 22 percent), and Philadelphia (up 7 percent).
Baltimore has seen a 60 percent increase over the same period.
"Why would cities be going in the same direction?" said Peter Scharf, a professor of public health at Louisiana State University who studies homicides in New Orleans. "It's hard, after 20 years of decline [in crime], to explain the upturn."
In New Orleans, Scharf pointed to factors such as police understaffing. The force has about 1,150 officers, far short of Mayor Mitch Landrieu's goal of 1,600.
Still, Scharf and others who study violence emphasize the need to address the roots of the problem. "You have to look at prevention resources as well as police resources," he said.
The importance of social services figured prominently in the discussion at the summit of big-city police chiefs this week in Washington, said Darrel Stephens, executive director of the Major Cities Chiefs Association, which organized the conference with D.C. Police Chief Cathy L. Lanier and others.
The group also discussed the need for alternatives to incarceration that could reduce recidivism among low-level offenders and the dangers of synthetic drugs linked to erratic behavior. And they called for stronger gun laws and stricter penalties for the use of high-capacity magazines.
"Cities are seeing a lot more rounds being fired on the streets at these homicide scenes," Stephens said.
Houston Police Chief Charles A. McClelland Jr. blamed criminals' access to guns. Legislatures around the county must be willing to give law enforcement more powers when it comes to limiting who can obtain a firearm, he said at a recent news conference.
"Our gun violence is just off the chart," he said.
The Chicago Police Department is taking steps to reduce the number of guns on the street, said police spokesman Anthony Guglielmi. Gun arrests are up 7 percent, and gun seizures are up 4 percent this year.
But he said the responsibility cannot rest solely with police.
"Frankly, we need help with this," he said, adding that judges, prosecutors and the community all play roles in keeping guns and repeat violent offenders off the street.
Kubrin, the professor of criminology, cautioned about speculating on the recent spikes, saying it's too soon to know if it is a trend. Still, she suspects that strained relations between police and communities are contributing to violence.
"You really can't effectively fight crime if you don't have a strong bond," she said. "The police depend on the community for help."
Some observers, including Baltimore's police union, have said police have been less proactive out of concern that they will be unfairly charged after six officers were indicted in Gray's death in April. The 25-year-old sustained a severe spinal cord injury in the back of a police transport van on April 12 and died a week later.
Homicides in the city have surged in the months following Gray's death. More than half of the city's nearly 200 homicides this year have occurred in the past three months.
A dramatic drop in arrests has also been blamed for the city's crime surge. The number of arrests plummeted more than 90 percent from April to May in several city neighborhoods, and more than 40 percent overall. From June to July, the number of arrests rose nearly 20 percent.
Jackson said this week that the focus in Baltimore — as in other cities facing turmoil that comes with rising violence — needs to be on urban reconstruction.
The city could put brick masons, painters, lead paint abaters and others to work if federal housing authorities devise a plan to deal with Baltimore's 16,000 vacant homes, Jackson said.
"You turn despair into hope," he said.
The federal government must be actively involved — in ways other than simply providing a military response, as was seen in Baltimore to control the rioting that followed Gray's death, Jackson said.
"Even at the highest level of the uprising, the focus was on more or less policing," Jackson said. "You kept waiting. Where's HUD? Where are the jobs?"
Harold Pollack, co-director of the University of Chicago Crime Lab, said the rise in violence should bring attention to some "fundamental long-term issues," such as youth employment in urban communities.
"Many Americans who are middle-class or affluent really don't fully appreciate the depth of the harm that was done in the Great Recession and how low-income communities are really suffering," he said. "Giving young people economic opportunities is giving them an alternative to the underground economy."
Baltimore Sun reporters Colin Campbell and Yvonne Wenger contributed to this article.