As a Philly police officer, I was a “rat” who exposed wrongdoing. And I paid the price.

Nothing in policing happens in a vacuum.

This is what I told a student at DeSales University in 2017. I was there to speak about my 25 years as a police officer in Philadelphia, and after my presentation, the student asked about combating what appears to be perpetual corruption and abuse in police departments.

In my response, I explained that “bad” law enforcement officers seldom operate in secret. The only way to limit or eliminate bad guys is for good guys to expose them. Yet, that “thin blue line” that illustrates how police officers keep communities from chaos becomes a solid blue wall that wraps around anyone who is willing to speak out about department problems. These “rats” become pariahs and they are either isolated or terminated.

Outing bad cops is a curse. I know, because I was a “rat,” and suffered for it.

Consider the recent conviction of Philadelphia Detective Philip Nordo for sexually assaulting informants (among other crimes). Based on my time as a Philly cop, I have no doubt others knew what Nordo was doing. But all kept silent. As a result, innocent people were imprisoned. Some were sexually abused.

In Memphis, silence around the culture of abuse in the Scorpion Squad enabled police officers to beat Tyre Nichols to death.

All of the people within the police departments who knew of problems but remained silent are complicit in these crimes.

For years, I complained to my supervisors and my Fraternal Order of Police representative about the standard practice of underreporting crime statistics, in which officers would try to persuade victims to back down. I witnessed Sex Crimes officers intimidating a 13-year-old girl whose father attempted to rape her; once they persuaded her to change her story, they downgraded the event to a domestic disturbance.

That practice was not unusual. But no matter how many times I complained, nothing changed until journalists began exposing the problem. In 1998, a serial rapist murdered Shannon Schieber, a Wharton doctoral student, and the department’s mistakes in handling the case further exposed its disturbing practice of downgrading sex crimes.

In February 1977, I provided my commander in Philadelphia’s 5th Police District information about a burglary ring involving on-duty police officers. This burglary ring had operated for years before my arrival in that district. Hundreds of citizens and businesses were victims. Because several citizens and members of the business community trusted me, they confided in me their frustration at being victimized by the people sworn to protect them. My commander did nothing.

I went to the Police Internal Affairs Bureau to report the burglary ring. After that, I believe I became the target of harassment that went on for years, designed to frustrate me into quitting. When I would answer calls that required more than one officer, no one would assist me; my transmissions via my police radio were constantly interfered with; my patrol sergeant fabricated department violations against me to have me terminated; I was sent from my district in Roxborough to as far away as South Philadelphia for fake “manpower” shortages.

Eventually, the frustration and anger I felt because of the retaliation faded, and I stayed on the job for 25 years. I retired from the Philadelphia Police Department in 1992.

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But I never forgot the lessons I learned from my time there.

Take any police scandal — for instance, the abuse of the Pennsylvania’s Heart and Lung Act, a generous disability benefit for first responders, which led to hundreds of cops getting full salaries while claiming they were unfit to work — and I guarantee there were people who knew what was going on and said nothing. That is the effectiveness of the blue wall of silence. It’s not a victimless crime: Hundreds of thousands of taxpayer dollars have been wasted on paying able-bodied police officers to stay home. That is fraud, and it’s a crime. When camaraderie hides criminality, the public is not served. These officers abandoned their public duty.

The culture of the blue wall of silence is modeled after the Mafia’s “Code of Omertà” and is meant for criminals, not law enforcement officers. That must end.

When camaraderie hides criminality, the public is not served.

Changing the culture of tolerating abusive and criminal activity by police officers must begin internally. That begins with better leadership and better psychological evaluations during the hiring process. Mandatory de-escalation and integrity in-service training must recur annually. To prevent officers from becoming “bad,” the department should monitor which units are associated with the most corruption (for instance, arresting innocent people to “show activity”), and prohibit any officer working more than two consecutive years in those units. (In my experience in Philadelphia, officers who spent years working on undercover assignments or anticrime units were the most likely to become jaded and corrupt over time.)

I am on the board of directors of the Lamplighter Project, an organization of law enforcement whistle-blowers. Any mayoral candidate or public official who desires to facilitate police reform should talk to us, the former cops who understand how the police code of silence works. We know how the resistance to positive reforms is ingrained in police culture and its bargaining units, and the details of how that resistance works.

We must tackle the blue wall of silence before we can replace it with voices of honor and reason. Until the police culture changes from protection for some to service for all, the city cannot count on its police force to keep residents safe.

Norman A. Carter Jr. is a retired Philadelphia police corporal who now lives in Georgia. He is the author of “The Long Blue Walk: My Journey as a Philly Cop.”