There are killers walking among us. Even though the homicide rate has shrunk to near record lows, there are more unsolved murders than ever. While law enforcement officials tout declining homicide rates, little is heard of abysmal "clearance rates."

There are killers walking among us. Even though the homicide rate has shrunk to near record lows, there are more unsolved murders than ever. While law enforcement officials tout declining homicide rates, little is heard of abysmal "clearance rates."

The clearance rate is traditionally defined by calculating the annual number of homicides solved divided by the number of homicides recorded in a given year. Each year, police departments across the country send their homicide statistics to the FBI. Each department reports the number of murders in a year and the number that were cleared in that year. The numbers are not necessarily related: Crimes cleared in one year might have occurred in a prior year.

A murder committed in 2012 and solved in 2013 affects the clearance rate for 2013. A city could end up with more murders solved in a year than were committed. In fact, one year Palm Beach County, Fla., reported a 114 percent clearance rate - 28 murders, 32 murders solved.

Even though the numbers as reported are alarming, there is some concern that they may be even worse. The Washington Post revealed in 2011 that the District of Columbia's clearance rate was "a statistical mishmash that makes things seem much better than they are."

Inevitably, more than 3 in 10 murderers are going to get away with their crime. Former New York City Police commissioner Raymond Kelly told the New York Daily News, "I think the clearance rate is going to remain at roughly 70 percent, give or take. That's just the way it is. There are ... certain homicides that will never be solved. We don't necessarily want to make that public, but that's just the way it is."

Nationally, the percentage of homicides that go unsolved has risen dramatically. In the 1960s about 90 percent of homicides were solved. According to the FBI, the average homicide clearance rate in the U.S. in 2012 was 62.5 percent.

There were 14,827 murders in 2012. Approximately 5,500 remain unsolved. Combine those with the nearly 185,000 cases of homicide that, according to a Scripps Howard News Service study, went unsolved from 1980 to 2008 and the numbers point to an alarming trend.

The question is why?

John Jarvis of the FBI Academy in Quantico, Va., and Wendy C. Regoeczi of Cleveland State University suggest that the dramatic decline in homicide clearance rates can be attributed to a number of factors. The expansion of defendant rights such as Miranda and increased legal constraints on police practices with regard to search and seizure have hampered investigative efforts.

They also cite changes in the nature of murder. There has been an increase in stranger killings - felony-related killings like drug deals gone awry and drive-by shootings.

Changes in societal factors such as community support for police have also impacted the ability to solve murders. Witness intimidation and the "no snitch" culture means fewer witnesses cooperate with police and fewer crimes are solved.

The limited resources available to local police departments, cut backs in training and the loss of a pool of talented detectives through retirement has also taken a toll on clearances rates.

Jerry Ratcliffe, a criminal justice professor at Temple University, told the Philadelphia Inquirer, America's gun culture has also contributed to the woeful clearance rates.

"As a nation, we have higher homicide rates and lower homicide-clearance rates than any westernized country, because we have almost nonexistent gun regulation," Ratcliffe said. "We allow people to kill each other at some distance. It's pretty difficult to have a drive-by stabbing, but it's really easy to have a drive-by shooting."

Whatever the reason, fewer killers are being apprehended and more of them are living, working and playing right in our midst.

Matthew T. Mangino is of counsel with Luxenberg, Garbett, Kelly & George P.C. His book "The Executioner's Toll, 2010" is due out this summer. You can reach him at www.mattmangino.com and follow him on Twitter at @MatthewTMangino.