The growing calls for systemic reform of American policing follow years of rising anger at the ongoing deaths of African Americans at the hands of law enforcement, including the recent killing of George Floyd.

The calls for change run the gamut from severely restricting police use of deadly force, creating a national database of abusive officers and re-directing taxpayer money away from police toward social programs that improve education and tackle crises including homelessness, poverty and mental health care.

But one key problem has gotten less attention: the conflict of interest, real and perceived, between prosecutors and police unions.

When district attorneys run for the office they get political donations from a range of interests including powerful, well-funded police unions who represent the officers that district attorneys will be called to prosecute in the event of officer brutality, corruption or even murder.

"We need to do everything that we can in this moment to avoid not only actual conflicts, to avoid the appearance of conflicts, if we hope to rebuild public trust and confidence in our system at a time when it is so, so sorely needed," says Diana Becton, the District Attorney of Northern California's Contra Costa County. She says the potential conflict of interest has exacerbated a crisis of trust in law enforcement and widened a sense the system is hopelessly rigged when it comes to prosecuting bad cops.

In a letter, Becton and a handful of other California district attorneys, including one DA candidate, are calling on the State Bar of California to ban "elected prosecutors – or prosecutors seeking election - from seeking or accepting political or financial support from law enforcement unions."

Historically, few police are prosecuted or convicted even when there's seemingly overwhelming evidence of excessive force.

The fact that few officers are held legally accountable only inflames tensions and widened that trust gap.

The examples are numerous: Eric Garner killed by police in New York: no indictments or criminal charges. Michael Brown shot by police in Ferguson, Missouri: no indictments. Freddie Gray's death in Baltimore police custody: no convictions. Stephon Clark shot by Sacramento police: no officer indictments or charges. And on and on.

Cities and counties do often reach out-of-court settlements with families of those killed, but few officers are held to account criminally.

Prosecutor Becton says this is not some hypothetical problem, it's a real one. She says even the perception of potential conflict undermines the system.

"I'm receiving money from their unions. And at the same time, I am going to be investigating possible incident instances of misconduct. Would you say, 'Hmm, I wonder if she's going to be fair to both sides?' " she asks. "So despite our best intentions, when we handle officer-involved cases, the public perceives conflicts of interest."

Activists and some attorneys have long called this kind of proposed rule change by state bars or legislatures vital to increasing police accountability.

Yet, little has changed.

"The relationship between the prosecution and the police is so problematic and it threatens any senses of due process and real equality in front of the law," says Nikki Jones a professor of African American studies and faculty at Center for the Study of Law and Society at U.C. Berkeley.

"We know that officers lie on the stand," Jones says. "We know that prosecutors know that they lie and still call on them. And that just threatens any belief or faith in a system of justice."

Chesa Boudin, San Francisco's district attorney, has joined Becton in calling for getting police union money out of prosecutor offices and political campaigns. He hopes this reform effort gains traction nationally and gets the attention of the American Bar Association.

"I think there's an opportunity for San Francisco and California to play a leadership role as the whole country is now focusing on what kind of reforms are necessary to restore trust between communities and law enforcement," Boudin says. "What sort of reforms are necessary to ensure equal enforcement of the law? We need systemic change, a new approach that ensures transparency and accountability. That will change the culture."

Yet, nation's highest court has repeatedly ruled that campaign spending is a form of protected speech.

The San Francisco Police Officers Association, the union representing rank and file officers, says this is simply an effort by a small group of liberal district attorneys and what the union calls "criminal apologists" to exploit the horrible death of George Floyd to score cheap political points.

Dustin DeRollo, a union spokesman, says it's telling that these prosecutors aren't also asking for DA candidates to stop taking contributions from criminal justice reform groups, well-heeled defense attorneys and private corporations.

"So if the concern truly was legal conflict of interest, how come they aren't addressing those issues? " DeRollo asked. "The reality is, as an officer of the court, as a district attorney, you should be able to set aside your politics from what you swore an oath to do. And if you can't do that, then turn in your bar card. Don't seek public office because that job's not for you."

The State Bar of California didn't respond to NPR's efforts seeking comment. The DAs who sent the letter say the bar has told them they are carefully reviewing their request.

But it's not clear when or if the nation's largest bar might take action to bring the hashtag #CureTheConflict closer to reality.

Copyright 2020 NPR. To see more, visit https://www.npr.org.