John Rappaport is a professor at the University of Chicago Law School. Ben Grunwald is an associate professor at Duke University School of Law.

During his five-year tenure with the Wauwatosa Police Department in Wisconsin, Joseph Mensah fatally shot three people. Mensah’s record is extraordinary, statistically speaking; most officers have never fired their weapon at all.

Mensah was suspended a few months after the third incident, which resulted in the death of 17-year-old Alvin Cole in February 2020. In October, an independent investigator — a former federal prosecutor — recommended Mensah’s termination to avert the “extraordinary, unwarranted and unnecessary risk” of a fourth shooting.

When the Milwaukee County district attorney declined to press criminal charges for Cole’s killing, protests erupted. Mensah resigned in November. Then, last week, Mensah was hired as a deputy at the nearby Waukesha County Sheriff’s Office. His appointment made national news.

But Mensah’s story is not unique. As American communities tackle police reform, they can and should take steps to prevent officers like him from being rehired. Consider these stories: Eddie Boyd III allegedly pistol-whipped a 12-year-old girl and falsified a police report in St. Louis before resigning and landing in Ferguson, Mo., of all places. Nicholas Hogan pepper-sprayed a suspect who was restrained on a hospital gurney; he was fired from the Tukwila, Wash., police, hired by a neighboring force, then fired again. Ryan Dubiel bounced among nine agencies in New Jersey until being convicted for simple assault. Timothy Loehmann resigned from the Independence Police Department in Ohio after a “dangerous loss of composure” during firearms training led supervisors to flag him as unable “to substantially cope, or make good decisions,” in stressful scenarios. He was then hired by Cleveland, where he shot and killed 12-year-old Tamir Rice. Even after that, another department tried to hire him.

Just how exceptional are these cases? Nearly 1 million sworn law enforcement officers are working nationwide, so even a few dozen awful stories might be played down as aberrational. And how problematic are they? Plenty of officers who have never been fired or resigned commit misconduct. Indeed, it’s not impossible that some officers who have been forced out of a job might be more careful than their peers.

We sought to answer these questions in a recent study by examining the careers of nearly 100,000 law enforcement officers employed in Florida over a 30-year period. We found that, in any given year, around 1,100 officers who had been previously fired were working for new Florida agencies. While these “wandering officers” represent a small fraction of all officers in the state, back-of-the-envelope calculations suggest they interact with hundreds of thousands of civilians each year. They tend to find work in smaller agencies with fewer resources in areas with slightly larger communities of color. And they’re roughly twice as likely as both officers hired as rookies and officers who’ve never been fired to lose their next job or receive a complaint for a serious “moral character violation.”

This problem is hard to solve because it involves multiple layers of government. One popular reform proposal, which we support, is to develop a national database of police misconduct, as proposed in the George Floyd Justice in Policing Act.

Yet a database helps only if agencies check it and care about what they learn. Cleveland never reviewed Loehmann’s file before giving him a gun. And the Waukesha sheriff knew Mensah’s story and hired him anyway.

The reasons officers like Loehmann and Mensah get hired are themselves complex. In some cases, agencies actually seek out cowboy cops to work the toughest beats. In others, they have difficulty recruiting better candidates. And in all cases, because their operational budgets are largely insulated from legal liability, agencies aren’t penalized when officers mess up — the victims of misconduct and taxpayers are.

In other words, knowing an officer’s history is one thing; caring about it is another.

A complementary approach involves officer decertification. Police in most states need professional certification to obtain lawful employment. Until recently, though, five states plus D.C. had no authority to decertify problem officers; another 20 states could decertify only after serious criminal convictions, which are extremely rare. Since the death of George Floyd, states have started moving in the right direction: Massachusetts and D.C. enacted decertification laws, California is considering one, and Iowa, Colorado, Oregon, New Mexico and Virginia have expanded their decertification powers. But even those with decertification power don’t always use it effectively. One study showed that in 2015, Mississippi and Wyoming did not decertify a single officer. In 2017, Louisiana hadn’t decertified one for misconduct in at least a decade.

These reforms are important, but they aren’t going to fix our broken system of policing, whose cracks reach far beyond the likes of Loehmann and Mensah. At the same time, if we can’t get this one right, where are we?

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