In recent years, law enforcement in the United States has been scrutinized on a bigger scale. The Associated Press just finished a year long investigation into sexual assault by police officers and the results are staggering. They uncovered "about 1,000 officers who lost their badges in a six-year period for rape, sodomy and other sexual assault; sex crimes that included possession of child pornography; or sexual misconduct such as propositioning citizens or having consensual but prohibited on-duty intercourse." Abuses that once may have been considered unrelated, solitary instances are now seen as relative. These officers aren't necessarily just bad apples—their crimes are part of a broader cultural issue and law enforcement agencies act like microcosms of society at large, reflecting structural inequality in the United States.

Dr. Phil Stinson studies corruption within law enforcement at Bowling Green State University. The former police officer is the head of a study by the Department of Justice called Police Integrity Lost: A Study of Law Enforcement Officers Arrested. "Almost all crime by police officers falls into one or more of these types: alcohol related, drug related, sex related, violence related, or profit motivated." Dr. Stinson explains that these crimes are hard to track for a variety of reasons. "There's no official statistics or data any agency keeps [on police crime]. Prior research in this area has been really hampered by various methodological problems; if you survey police officers and police departments there's a social desirability effect. They're not going to answer these questions honestly."

The case of former officer Daniel Holtzclaw is an especially egregious example of a law enforcement official's abuse of power to brutalize women. Holtzclaw is on trial today for the sexual assault of thirteen African American women.

If the allegations are true, it's clear to me that in his mind that not only are these people vulnerable, but he's a predator.

"Daniel Holtzclaw has taken it to an extreme," says Dr. Stinson. "These are just allegations still, he hasn't been convicted yet, but every one of his potential victims are African American women, and they're typically older than I would have expected." Dr. Stinson's research shows that the victims of police sexual assault are disproportionately underaged. "If the allegations are true, it's clear to me that in his mind that not only are these people vulnerable, but he's a predator. These are women he views as throwaways."

While these crimes sometimes appear as outliers, Dr. Stinson says they're far more common than we think. Its hard for a victim to come forward with allegations because they may not feel safe to do so. But getting the story out there is crucial. "When one woman, one girl, or even a boy is believed, and it gets charges brought and it gets in the newspaper—for every one victim that comes forward initially, there's five more that come forward. That's what happened with Holtzclaw."

When a claim is taken seriously, the cases may never become public; police departments often deal with the issue behind the scenes. "Sometimes [officers are] given the opportunity to resign in lieu of being criminally prosecuted. One of the reasons they have to do that is if they question an officer and they ask him about an incident and they require him to answer the questions, they have to elect that they're going to use the statements administratively or criminally. Once they've decided to use [testimony] for discipline purposes, they can't use those statements against the officer in court. They have to build their criminal case another way."

The issue of police sexual assault is erased in other ways, too. "In some cases instead o charging an officer with a sex crime, they'll charge him with official misconduct or official oppression or violation of oath. It hides the true nature of the crime, so they might get convicted, but they're not a registered sex offender."

For every one victim that comes forward initially, there's five more that come forward.

As a former police officer, Dr. Stinson has seen corruption firsthand. When he was working in New Hampshire in the 80's, he and a few other officers arrested a man with possession of child pornography. "The sergeant that I worked with at the time spent the next month cataloguing and watching every one of the videos. It was clear to me that he had more of an interest than he should have in these cases."

Sexual violence by police officers is targeted at vulnerable demographics, at people whom the cop can most easily control. "Holtzclaw is a league of his own. What's more common is the cops who are abusing, harassing, tormenting, torturing, women who work in the sex trade."

Dr. Stinson has a theory that policing is "sexual." "There's a sexual dynamic to it," he says. "It's a twisted power and coercion dynamic, [and it can be] a complete misuse of authority and power." An officer may encounter sex-related issues throughout their work. "It's a reoccurring theme. They deal with sex crimes, they're surrounded by vulnerable people, there are all these different aspects. Power equals sex in many ways. It's something that is not talked about; there things we don't discuss in polite company."

Read more: Rikers Staff Almost Never Report Inmate Sexual Abuse to the Police

Because it has been largely erased from public records, it is challenging to study this subject matter—which contributes to its erasure and the fallacious idea that law enforcement is, as Dr. Stinson says, above law enforcement. The culture of silence and the imbalance of power are two parts of an institutional system of oppression. Even the researcher confronts obstacles: Studying police corruption has alienated Dr. Stinson from old friends in the force.