In the last year, The Washington Post has gathered data on almost 55,000 murders over the past decade in 55 of America’s largest cities. The analysis goes beyond what is known nationally about the unsolved cases, revealing block by block where police fail to catch killers.

The Post’s biggest findings

Fifty percent of the murders The Post examined did not result in an arrest.

Despite a nationwide drop in violence to historic lows, 68 percent of cities have a lower homicide arrest rate now than a decade ago.

Black victims, who accounted for the majority of homicides, were the least likely of any racial group to have their killings result in an arrest.

Major police departments with high arrest rates generally have detectives working on fewer than five homicide cases annually.

Police say poor relationships with residents make it more difficult to solve homicides. In many cases, police say they know a killer's identity but cannot get witnesses to cooperate out of fear of retaliation or mistrust of law enforcement.

Nearly half of female victims who were murdered during the past decade were killed by a current or former intimate partner. An analysis of five cities showed there were often warning signs that these women were in danger.

Two-thirds of solved homicides saw an arrest within one month. For cases that remained unsolved after one year, 5 percent ultimately led to an arrest.

Using public records requests, The Post acquired detailed information about up to a decade of homicides: victim information, location and whether an arrest had been made in the case. Once analyzed, The Post's data offered the most detailed public look available into big-city homicide.

The database

As part of this investigation, The Post compiled and mapped up to a decade of homicide arrest data in 55 cities. We identified neighborhoods where murder is common but arrests are rare. We also showed how arrest rates vary among races in each city.

Explore the maps

The series

Dalton Bennett/The Washington Post

Where killings go unsolved

The Post mapped nearly 55,000 homicides in major American cities over the past decade and found that across the country, there are areas where murder is common but arrests are rare.

“If these cases go unsolved, it has the potential to send the message to our community that we don’t care,” said Oakland police Capt. Roland Holmgren, whose city has two areas where unsolved homicides are clustered. Read the story.

Podcast: Unsolved, but not a mystery

Activists and the Boston police commissioner participate in a neighborhood peace walk in July. (Yoon S. Byun for The Washington Post)

An unequal justice

In the past decade, nearly 26,000 murders have gone without an arrest in major American cities. Of those, more than 18,600 of the victims — almost three‑quarters — were black. In many cases, there is a distrust between the police officers trying to solve these murders and the communities where they happen.

In Indianapolis, 69 percent of those killed are black, while 24 of 30 homicide detectives are white.“I think there’s an expectation that their police department, or those public servants, look like a representative of the people that they serve. So right off the bat, we don’t look like the community that we serve in that area,” Police Chief Bryan Roach said. Read the story.

Podcast: The cycle of impunity

Dalton Bennett/The Washington Post

Buried under bodies

Even with murder rates falling, big-city detectives face daunting caseloads. For many, new homicides are coming in faster than detectives can solve them. Read the story.

Re-assigning detectives to help reduce homicide caseloads: The Detroit Police Department said it has increased the number of homicide detectives it employs following The Post’s story detailing how the department and others in the nation have struggled to make homicide arrests amid high detective caseloads. Read the story.

Deangelo Norwood was severely injured when he was shot in late July in Chicago. (Whitten Sabbatini for The Washington Post)

‘Ain’t nobody been locked up.’

More than 2,000 people will be shot in Chicago this year. Most will live, but most of their shooters will never be caught. Read the story.

Dalton Bennett/The Washington Post

Witness to the killing

In many homicides, police believe they know the killer's identity but can't get a witness to cooperate.

Shameek Massey, who was asked by police to testify after her husband witnessed a murder, talked about the ramifications of cooperating with police. “It wasn’t that I didn’t want to do the right thing,” she said. “It was what could come afterward — having to move, my kids having to move.” Read the story.

Khaalid Muttaqi, director of the Gang Prevention and Intervention Task Force in Sacramento. (Mason Trinca for The Washington Post)

Trying to stop a killing before it happens

Gang-related violence accounts for more than a quarter of Sacramento’s homicides. City officials have recently focused on intervening directly with young men who are closest to the violence — including known shooters — before they either pull the trigger or become a victim themselves. The controversial program uses cash incentives as part of its work to end this type of violence.

“When it comes to working with the younger kids, everyone is on board,” said Khaalid Muttaqi, director of Sacramento’s Gang Prevention and Intervention Task Force. “But when it comes to the harder grind, working with the guys already in the gangs, some people have trouble accepting it.” Read the story.

Cynthia Glover on the porch of her home in New Orleans. (Edmund D. Fountain for The Washington Post)

In a home surrounded by homicide

In New Orleans, where police make an arrest in only a third of homicides, Cynthia Glover, 56, lost three children to murder. Now she fears for her last.

“You got countless mothers like me who have lost their children, and nobody have done nothin’. They give you a candlelight vigil. They let go of some butterflies and some balloons and feed you some cake. But at the end of day, that don’t change the fact your child ain’t never coming back here,” Glover said. Read the story.

Podcast: Surrounded by homicide

Minerva Cisneros was shot in the chest by the father of her children. (Ilana Panich-Linsman for The Washington Post)

How domestic violence leads to murder

The Washington Post found that nearly half of the women who were murdered during the past decade were killed by a current or former intimate partner; in five cities, about a third of these male killers were known threats. Read the story.

A mural depicting Freddie Gray is seen in Baltimore. His death in police custody continues to reverberate across the city. (Salwan Georges/The Washington Post)

An ‘open season for killing’

Homicide rates have soared in Baltimore, but the number of arrests have plummeted. Police and community leaders say the issue has roots in police mistrust and overwhelming caseloads. Read the story.

An old newspaper clipping is taped to the wall of a Phoenix detective’s cubicle. (Caitlin O'Hara for The Washington Post)

When finding the killer becomes nearly impossible

A Washington Post examination of 8,000 homicide arrests across 25 major U.S. cities since 2007 found that in half of the cases, an arrest was made in 10 days or less. For cases that remained open after one year, only 5 percent led to an arrest.

In Phoenix, eight years after the seemingly random slaying of 13-year-old Jonathan Garcia Valladares, police have no motive and yet to make an arrest in what has become another puzzling cold case in their backlog of thousands. Read the story.