Authored by Ryan McMaken via The Mises Institute,

One of the central arguments in favor of the government's monopoly on police powers is that government police are essential in "keeping us safe." Without this "thin blue line" between chaos and order, we are told, society will descend into chaos.

How exactly this order is maintained by police, however, is less clear. In recent years, police agencies have insisted they have no legal obligation to directly intervene to protect people from threats posed by criminals. The courts have agreed.

Having abandoned the "protect" part of "to serve and protect," the police have retreated to the claim that their real role is simply to "enforce the law." This "enforcement" presumably would include investigation of crimes and arrests of suspects.

So how is that going for them?

According to the most recent FBI "Crime in the United States" report, only 45 percent of violent crime lead to arrest and prosecution. That is, less than half of violent crimes result in what is known as a "clearance" of the crime. Property crime clearances are much worse. Only 17 percent of burglaries, arsons, and car thefts are "cleared."

Among violent crimes, homicides experience the highest clearance rate by far, at 61 percent. Aggravated assault comes in at 53 percent, and rape at 34 percent.

But these are just cases where arrests are made and prosecutions are initiated. A smaller number of cases actually lead to convictions. A crime may be cleared even when the suspect is later exonerated.

According to the Bureau of Justice Statistics, the nationwide conviction rate for murders is 70 percent.

So, we may be looking at a situation in which for every 100 homicides, 61 percent are cleared, and then 70 percent of those — 43 cases — lead to conviction. And this assumes that the correct person is convicted. According to some estimates, four percent of inmates on death row are innocent. Wrongful conviction rates are assumed to be higher for lesser crimes since officials are less rigorous in establishing guilt when capital punishment is not on the table.

These are all aggregate estimates, of course, but it's not outlandish to conclude from the available evidence that at least half of homicides don't lead to conviction of the guilty party. Convictions for other sorts of crimes are well below that.

Moreover, clearance rates for homicides and other crimes are far below the national average in certain places.According to Peoria, Illinois' Journal-Star, "the Murder Accountability Project was able to determine the state’s 2015 clearance rate at roughly 37 percent. By comparison, Peoria cleared 47 percent of its cases that same year."

Meanwhile, Boston's police department recent increased its clearance rate to slightly above the national average, but this "followed a five-year period, from 2007 to 2011, when homicide detectives had cleared only 148 of 314 killings, with a clearance rate of 47 percent."

With so few homicides leading to convictions, it's not surprising that one criminologist has described the situation as "a national disaster."

Better Police Work Can Lead to Better Outcomes

Part of the reason that low clearance rates are alarming is that they create the conditions that lead to fewer clearances in the future. For example, if witnesses believe the police are unlikely to actually arrest and prosecute the guilty parties, witnesses are more likely to be too frightened to come forward. In the case of lesser crimes, such as sexual assaults and burglaries, many victims may conclude the unlikelihood of a conviction make reporting crimes not even worth the trouble.

Police agencies are often quick to point out that many of these issues are beyond their direct control. And, some factors beyond police control can make some cases very difficult to investigate. If the victim was a member of a gang, for example, finding cooperative witnesses will be very difficult indeed. If the crime was part of a drug deal, this makes things much harder for investigators as well.

But there are also plenty of factors well within the control of police. As noted by researchers Anthony A. Braga Desiree Dusseault,

Factors that were within police control and exerted significant influence on whether homicide cases were cleared included the actions of the first officer on the scene, response time less than 30 minutes, the notification of the crime lab and medical examiner’s office, the number of detectives assigned to the case, detective follow-up on information provided by witnesses, computer checks on involved individuals and any guns in the case...

In a study by B. Forst, J. Lucianovic, and S. J. Cox, the authors

discovered that officers with the most arrests and convictions commonly re-sponded most rapidly to calls for service, were better crime scene managers, were best at identifying, locating, and questioning witnesses, and displayed more of the characteristics commonly identified as relevant to successful investigators. In addition, Forst discovered that cases in which an arrest was made within 30 minutes after the case was reported had the highest chance of resulting in a conviction

Forst, et al, also found that "a relatively small number of officers make a disproportionate number of arrests that result in conviction."

That is, a small subset of police personnel made arrests that were of higher quality than other officers. These, we might conclude, were the most competent officers who engaged in the most rigorous police work described above: finding witnesses, managing a crime scene, responding quickly, etc.

Assigning more police resources to cases helps with outcomes as well. According to a report for the National Institute of Justice:

The data indicate that the number of detectives assigned to a case is particularly important: Assigning a minimum of three detectives and perhaps four appears to increase the likelihood of clearing it. ... The city with the consistently highest clearance rates also was the city that was much more likely to devote 11 detectives during the initial days of investigation.

In practice, however, few police departments are willing to devote these sorts of resources to most homicide cases.

The most common rationale given for this inattention to the most violent crimes is that police agencies are already stretched too thin to address every crime.

But is this a valid excuse?

Perhaps not when we note how little of police time and resources are spent on addressing violent crime.

According to the Vera Institute of Justice, "fewer than five percent" of arrests

are for serious violent crimes. Instead, the bulk of police work is in response to incidents that are not criminal in nature and the majority of arrests involve non-serious offenses like “drug abuse violations”—arrests for which increased more than 170 percent between 1980 and 2016—disorderly conduct, and a nondescript low-level offense category known as “all other non-traffic offenses.”

These offenses are behind 80 percent of all arrests.

Put a little differently: criminologist Victor Kappeler concludes that per capita, police make 14 arrests per year. But, "less than one of these arrests would have been for a violent crime and fewer than two arrests would have been for property crimes. In fact, 12 of the arrests made by our “average” police officer would have been for petty crimes like minor drug or alcohol possession, disorderly conduct, and vandalism."

This should not be shocking when we consider how police departments work. From a professional standpoint, spending long hours on a small number of violent offenses is not a good way to move up in the ranks. Police departments often base promotions and pay on number of arrests made, and other metrics which drive personnel toward making easy arrests for easily-observed offenses.

As noted by William Waegel in an article on police procedures, police personnel were driven by expectations for "production of investigative reports" and "two or more arrests per week." Thus, cases unlikely to lead to quick arrests were "skimmed" in which hard-to-solve cases were deemed "routine cases" and "given little attention."

From this perspective, busting a ring of skilled burglars, or hunting down a gangland killer, brings few advantages. Moreover, making a small number of homicide arrests doesn't help departmental revenues as do drug busts that can bring with them lucrative seizures through asset forfeiture laws.

This helps explain why - as shown by this analysis at mises.org - many police agencies spend enormous amounts of time tracking down suburban pot smokers while thieves and thugs go un-investigated.