Editor’s note: This is the 12th article in a collaborative series with the R Street Institute, exploring conservative approaches to criminal justice reform.

Over 2,000 people have been exonerated from criminal convictions since 1989. But to blame mere incompetence or simple negligence would be a mistake. In the majority of these cases, it was criminal or unethical behavior by witnesses, law enforcement, and even the government that put these individuals behind bars in the first place.

Without emphasizing integrity and accountability in the criminal justice system there will never be true reform. After all, 52 percent of these exonerations involved official misconduct, according to the National Registry of Exonerations.

While it would be quite difficult to find a case in which law enforcement took illegal measures to free a guilty man, we’re inundated with a litany of scandalous conduct by law enforcement and prosecutors apparently willing to bend the rules to make sure potentially innocent people never see the light of day.

Earlier this year, the Miami Heraldreportedthat former Biscayne Park police chief Raimundo Atesiano was obsessed with having a perfect clearance rate for property crimes. In turn, his staff reportedly told officers if they “see anybody black walking through our streets and they have somewhat of a record, arrest them so we can pin them for all the burglaries.”

As a result, a series of people were framed for crimes, including Erasmus Banmah, who was falsely arrested for five auto burglaries. The arresting officer admitted that he lied in his report that Banmah confessed to the burglaries and gave details about the crimes.

Following an investigation the former police chief was sentenced to three years in prison. That’s actually less time received than one of the men falsely convicted for a home burglary under Atesino’s direction. Clarence Desrouleaux was sentenced to five years and deported to Haiti. (Due to evidence from this scandal, Desrouleaux’s conviction was later thrown out by the Miami-Dade State Attorney’s Office.)

These stories are not uncommon in police departments across the country. The New York Times ran a series earlier this year about police perjury, or as it is unofficially known “testilying.” The Times identified 25 cases in New York City over the last three years in which officers were suspected of lying under oath.

Writer Joseph Goldstein accurately pointed out that the 25 cases are only a fraction of the known malfeasance because most cases result in a plea deal. He quoted an unnamed officer who said, “There’s no fear of being caught. You’re not going to go to trial and nobody is going to be cross-examined.”

Even if they are caught, the justice system tends to be lenient with corrupt cops. Two weeks after this report, a New York City police officer was sentenced to a mere three years of probation after being convicted of perjury.

This has been a fairly persistent issue for decades. Nearly a hundred cases were thrown out in New York for police perjury after the Mollen Commission in 1994. The Mollen Commission concluded, “Perjury is perhaps the most widespread form of police wrongdoing facing today’s criminal justice system.” So why are we still talking about it more than 20 years later?

Meanwhile, the issue of tainted evidence goes beyond perjury and false statements. Police have also been caught planting evidence. There’s even an informal term for this practice called “flaking.” This video released last month by The New York Times appears to show this taking place.

A Baltimore police officer was indicted earlier this year after bodycam footage showed him planting evidence in a drug arrest. Since bodycams are more prevalent now, one would think it might cut down on this illicit practice—or cops might get more crafty.

But planting evidence is only the tip of the iceberg. Take Andrew Wilson, who Loyola Law School’s Project for the Innocent helped exonerate after spending 32 years in prison for a wrongful murder conviction.

The prosecution in his case withheld key evidence. In particular, Wilson was selected out of a lineup of suspects by the eyewitness to the murder only after a LAPD detective pointed specifically to Wilson’s picture and asked, “What about him?” Bear in mind, she had pointed previously to two other suspects.

This kind of suggestive form of evidence collection has no place in the judicial system. However, it’s one of the reasons why mistaken witness identifications are a contributing factor in 29 percent of exonerations, according to the National Registration of Exonerations.

The most common factor in an exoneration—occurring 57 percent of the time—is perjury or a false accusation by police and informants.

False testimony from confidential informants led to David Robinson’s murder conviction in Sikeston, Missouri, in 2001. Robinson was arrested for the crime, but he was released shortly thereafter when the physical evidence didn’t connect him to it.

However, the lead detective, John Blakely, found a paid informant and inmate in the local prison who wrote a statement claiming to have witnessed Robinson commit the murder. Consequently, the informant was immediately released, placed into witness protection, and eventually received $2,000. He later admitted that he lied in order to get out of jail.

Another jailhouse informant, Jason Richison, said that he shared a cellmate with David Robison and heard him confess to the murder. Years later, Richison accused detective Blakely of coercing his statement through threats and abuse.

Worst of all, the actual killer, Romanze Mosby, confessed while behind bars: it was a drug deal gone wrong. He was serving a 10-year sentence for assault at the same prison where Robinson was incarcerated and the guilt led Mosby to eventually commit suicide.

In short, Robinson was released three months ago, which means he lost 18 years of his life. On the other hand, the punishment for detective Blakely was much less severe: he was placed on leave.

To be clear, inmates are allowed to come forward with information about crimes in exchange for leniency. However, government officials can’t enlist informants to target specific people, otherwise, they’d be working in a law enforcement capacity.

That’s the crux of what is known as the “Orange County snitch scandal.” This scandal was revealed in the high-profile murder case of Scott Dekraai who killed eight people in a mass shooting at Seal Beach in 2011.

An informant was placed in the cell next to him with a recording device. The Dekraai case led to the discovery that Orange County sheriffs had used similar covert investigations via informants for nearly 30 years. Independent investigators have found that the sheriffs lied or willfully withheld information about their informants in 146 cases.

The prosecution didn’t need tainted evidence in such an open and shut case as Dekraai’s to gain a conviction. However, the scandal led to several dubious convictions, including Thomas Thompson, who was convicted and executed in 1998 primarily as a result of testimony from two non-credible jailhouse informants.

60 Minutesinterviewed a former Orange County inmate, Mark Cleveland, who was placed in cells next to several high-profile targets to gain evidence. Cleveland was rewarded with having 40 years shaved from his sentence, and he’s now a free man. However, he did admit that “a lot of my information was probably—maybe tainted.”

Unfortunately, prosecutors can usually get away with shady practices involving informants because cases usually end in plea bargains. In fact, in the U.S. Supreme Court case United States v. Ruiz, it was ruled that defendants are not entitled to information impugning the credibility of a confidential informant unless the case goes to trial.

That’s a terrible precedent considering the powerful incentives for informants beyond just reduced sentences. The DEA’s highest-paid informant, Andrew Chambers, earned over $4 million for his work on 280 cases. He was deactivated in 2000 because it was revealed publicly that he had committed perjury in those several cases. Nonetheless, Chambers was reactivated by the DEA in 2013.

The DEA now has a network of 18,000 informants who earned $237 million from 2010 to 2015. Suffice it to say, the combination of reduced sentences, financial incentives, and the low-evidence requirement for conspiracy drug cases is a recipe for widespread injustice.

Informants have been caught planting evidence, but often their testimony alone is enough for a conviction. There are too many draconian examples to list succinctly, but a PBS film, Snitch, perfectly encapsulates the severity of the problem.

All this is to show there is a clear crisis of credibility within the criminal justice system. Not everyone is part of this win-at-all-costs culture. However, that contingent is far too representative, and they are hardly held accountable, making it a self-perpetuating injustice.

Brian Saady is the author of four books. That includes his series, Rackets, which chronicles the legalization of drugs and gambling, and the decriminalization of prostitution. You can check out his podcast and follow him on Facebookand Twitter.