On Wednesday, D. Watkins, an author and essayist who grew up in Baltimore, wrote an op-ed article in The New York Times saying that police brutality in Baltimore and other U.S. cities is due, in part, to police officers living outside the communities they serve.

“The police officers in Baltimore, as in many places in the country with dense black populations, are out of control, have been out of control,” he wrote. “One of the major reasons is that many Baltimore police officers don’t live in Baltimore City; some don’t even live in Maryland. Many don’t know or care about the citizens of the communities they police, which is why they can come in, beat us and kill us without a sign of grief or empathy.”

Residency requirements for police officers have long been championed by politicians and activists as a way to bind a police force with its community, but it is not at all clear such requirements are effective at doing so. As we wrote in October, the requirements may have a significant downside. Paradoxically, residents of cities where officers are required to live within city limits also tend to have less confidence in the police. And the police forces themselves tend to be less racially representative of the cities they serve.

Experts attribute these problems to recruitment. Placing a restriction on where officers are allowed to live also ends up restricting the pool of applicants, making it less diverse and possibly less capable.

Last August, while protests were happening in Ferguson, Missouri, we looked at the U.S. cities with the largest polices forces, and what percentage of each city’s officers live within city limits. In Baltimore in 2010, almost 3 in 4 police officers didn’t live in the city proper, and that number was even higher for white officers.