Research from Bowling Green State University (BGSU) claims that, over a nine-year period, police officers in the U.S. were charged with over 400 rapes.

According to the research, which can be found here, officers in the U.S. were charged with forcible rape 405 times between 2005 and 2013. That’s an average of 45 a year. There were 636 instances of forcible fondling.

Experts say the statistics on sexual assaults by police are almost nonexistent.

“It’s just not available at all,” said Jonathan Blanks, a research associate with the Cato Institute’s Project on Criminal Justice. “You can only crowdsource this info.”

BSGU researchers gathered their list by documenting cases of sworn nonfederal law enforcement officers who have been arrested, according to WTVF. However, the federally funded 2016 paper, “Police Integrity Lost: A Study of Law Enforcement Officers Arrested,” claims the problem isn’t limited to sexual assault.

“There are no comprehensive statistics available on problems with police integrity,” the report says, and no government entity collects data on police who are arrested.

It adds, “Police sexual misconduct and cases of police sexual violence are often referred to as hidden offenses, and studies on police sexual misconduct are usually based on small samples or derived from officer surveys that are threatened by a reluctance to reveal these cases.”

Researchers typically rely on published media reports. Numbers gathered by BGSU are the result of Google alerts on 48 search terms entered by researchers.

The reports of police assault are lacking for multiple reasons, but one of the biggest is the victims’ reluctance to report the crime.

“Who do you call when your rapist or offender is a police officer? What a scary situation that must be,” said Philip Stinson, an associate professor of criminal justice who served as principal investigator for the police integrity paper and whose research assistants maintain the BGSU database.

Data is lacking for many reasons. The federal government cannot force state law enforcement agencies to contribute the numbers. Even if that were possible, the Justice Department wouldn’t have the resources to oversee and maintain such a database.

Unions also work hard to protect police officers and their reputations.

“They don’t want their officers and membership shamed if something goes wrong,” Blanks said.

Legal hurdles can arise in trying to obtain even basic cases, “and that’s on purpose,” he said. Some states’ laws shield the identities of police officers who commit crimes, he said, while some jurisdiction include nondisclosure agreements in victim settlements.

“The system is rigged to protect police officers from outside accountability,” Blanks said. “The worst cops are going to get the most protection.”

Also, victims include suspects and the people police are supposed to protect, which makes reporting difficult.

According to WTVF, one statistic from Stinson indicates that for every sexual assault that makes the new, there are almost always more victims–on average, five more.

About half of those victims are children, researchers said. Stinson claims he has gotten accustomed to hearing his research assistants proclaim during their work, “Oh, my God, it’s another 14-year-old.”

“Opportunities for sex-related police crime abound because officers operate in a low visibility environment with very little supervision,” it says. “The potential victims of sex-related police crime include criminal suspects but also unaccompanied victims of crime.”

Experts say officers who prey on people they encounter while on duty take advantage of the trust the public places in police as an institution.

“Police have a reputational advantage over anyone, especially someone accused of a crime,” Blanks said, explaining that a regular Gallup poll shows again and again that police are third only to the military and small business owners in terms of trust. “People want to believe the police.”

Victims typically fall into at least one of six categories, according to researchers. They have criminal records, are homeless, are sex workers or have issues with drug or alcohol abuse. The officers committing these crimes “are picking on people who juries won’t believe or who don’t trust police,” Stinson said.

These crimes can have a ripple effect despite the fact that, according to the experts interviewed, the majority of officers are good people, not sexual predators.

However, this problem is much larger than individual officers, said author and former Seattle Police Chief Norm Stamper.

“I think it’s a huge problem,” he said. “In reality, there’s probably no law enforcement agency that has not had this problem.”

“It cheats good cops,” he said. “If a police officer is arrested for having fondled a DUI suspect in a jurisdiction, that affects all officers.”

Issues of trust are further exacerbated by the “blue wall” of silence that’s put up when an officer is accused of a crime, he said. It’s expected, Stamper continued, because officers rely heavily on one another, especially in dangerous situations. Telling on a colleague could mean trouble for an officer the next time he or she needs backup.

“If I’m a snitch, then the chance that my fellow officers will not have my back is significant,” the former police chief said.

Stamper, and some others, believe the solution lies in revamping police culture.

“The paramilitary, bureaucratic structure produces a dysfunctional culture,” Stamper said, and added that for one of the “most delicate and demanding” jobs in America, officers largely go unsupervised.

Specific to sexual assault, experts would like to see departments enact:

- Policies “to make victims feel safe,” Stinson said, which could include online or anonymous reporting and special officers trained in dealing with sexual assault victims

- GPS tracking of officers, especially those with take-home vehicles, and monitoring of officers. If a supervisor notices a patrolman predominantly stops women between the ages of 18 and 30 at the same time of night in the same part of town, it would raise red flags

- Rules forbidding departments from hiring officers who were fired from other agencies, which happens too frequently, Stamper said

- Mandates that officers must activate their bodycams and dash cams and be punished if they don’t. (This will actually vindicate officers more often than not, experts say)

- Occasional sting operations, involving internal affairs, aimed at ensuring police officers are appropriately interacting with the public

“It’s critical supervisors trust officers, but trust is earned,” Stamper said, adding that the job is too important to trust officers blindly.

The police chiefs and sheriffs defending bad cops erodes trusts, Stamper said. He said he’s frustrated every time he sees a police executive step to a podium to decry the “bad apples” responsible for a crime that has tainted a department.

“If they repeatedly go back to that bank of microphones to bemoan the bad apples, it’s time to look at the barrel. … Look at the orchard,” he said.

Experts say that accountability it essential in changing the culture.

Uniformity, via the licensing of individual officers and the certification of police departments, is key, Stamper believes.

He said, all 18,000 police departments operate under their own rules, based on their traditions, policies, procedures and recruitment methods, Stamper said. Creating national standards could improve the quality of policing.

If a licensed officer were to violate someone’s rights–by illegally searching or arresting them, manipulating evidence, using unnecessary force, or engaging in sexually predatory behavior–that officer’s license would be revoked.

Until America changes the nature of the conversation around policing, things are destined to remain the same when it comes to criminal cops, Stamper said.

“The forces of resistance are powerful,” he said. “If you push the system, it’s going to push back with equal or greater force.”