While homicide clearance rates have declined across the nation from about 90 percent in the 1960s to below 65 percent in recent years, some police departments have bucked the trend.
Many of those police departments, including those in Durham, N.C., Santa Ana, Calif., and Polk County, Fla., are using cutting-edge murder-investigation techniques.
"We think that all departments could improve their clearance rates if they would provide a priority to homicide clearances and begin to use these best practices that are slowly emerging from the research base," concluded University of Maryland criminologist Charles Wellford.
Among the most common recommendations by criminology scholars and Department of Justice researchers to improve homicide investigations:
-- Make homicide clearance a priority. Keep track of the department's clearance rates. Apply additional resources such as increased manpower or improved training for investigators to clear a backlog of cold cases. If necessary, create a specialized cold-case squad or, better, a multi-departmental cold-case task force.
When clearance rates dropped to 42 percent during the 1990s, Santa Ana asked for federal grants to hire extra detectives to work the growing numbers of unsolved homicides. The clearance rates rose to 69 percent since 2000 -- the third-best improvement for any major police department, according to a Scripps Howard News Service study of FBI homicide records.
"We had a federally funded cold-case project about 13 years ago. Everyone saw how successful it could be," said Santa Ana Police Chief Paul M. Walters.
-- Make sure homicide supervisors keep track of open cases through so-called "compstat" analysis -- usually, computer-based tracking to provide a multilayered approach to personnel and resource management of local crime. Hold regular meetings with homicide investigators. Departments making effective use of Computerized Case-Management Systems (CCMS) were documented to have at least a 5 percent improvement in homicide clearance rates, according to one FBI study.
"Accountability is the key," said Philadelphia Deputy Police Commissioner Richard Ross. "Homicide departments don't run themselves. There's nothing like having to sit in front of your captain and explain the status of every case."
Philadelphia adopted its own compstat system when city officials declared a crime emergency after homicide clearances dropped to 56 percent in 2006. They rose to 75 percent by 2008.
-- Make sure there is sufficient manpower at the crime scene, especially during the first minutes after the discovery of a killing. The latest Justice Department recommendations suggest that a minimum of two, two-person teams be sent to the scene as quickly as possible. Large police departments that regularly send eight or 10 experienced investigators to the scene have produced above-average clearance results.
"We know that the longer the period awaiting an arrest, the less likely that arrest will be," said Polk County, Fla., Sheriff Grady Judd. "We send a team of four to eight supervisors, homicide detectives and crime-scene technicians to the scene. And we work the cold cases, too."
Detectives in Polk County east of Tampa were solving only 56 percent of homicides during the 1990s. But new priorities and investigative techniques pushed clearance averages to 84 percent in recent years -- the second-largest improvement in the study.
-- Make sure investigators get the time needed to solve murders. Don't be stingy with overtime, especially when investigators are in hot pursuit of evidence. Departments that allow senior detectives to approve their own overtime have a 9 percent higher clearance rate, according to FBI data.
"That's something I've been yelling about for years. So now we authorize the payment of overtime so investigators don't have to worry about being compensated while working the big cases," said Durham, N.C., Police Chief Jose Lopez.
Durham experienced the nation's largest improvement in homicide clearance rates, rising from 39 percent in the 1990s to 78 percent since 2008 thanks to a number of reforms.
Crime experts and veteran cops also recommend:
Be generous with training. Make sure investigators know the current best practices through so-called "in-service" training rather than assuming they learned everything at the police academy.
Make sure the first responders -- beat cops who usually are the first to a homicide scene -- know how to protect evidence, identify witnesses and assist in neighborhood canvasses for witnesses. It is critical that they know whom to call -- detectives, medical examiners and crime-scene technicians -- in the first minutes of an investigation.
Make best use of information technology. Probably most important is automated information-sharing between homicide detectives, narcotics investigators, gang specialists and street intelligence units. Killers and associates of killers often have a long and detailed history with local police.