Transcript for St. Louis prosecutor on why she filed a complaint against city, police union
Reporter: Essentially, you are accusing the city government, city police, and in particular the police union of a conspiracy of racism, directed to stop you dead in your tracks. I had no choice but to act for the will of the people because they want me to fight for what's right. Reporter: Kim Gardner, the first black prosecutor ever elected in St. Louis, just dropped a bombshell. An explosive lawsuit accusing the city and the police union of a racist conspiracy aimed at stopping her from doing her job. This is not about Kim Gardner. This is about implementing the reforms that's needed in our community. Reporter: She's brought reforms to her office that have made her enemies all across the state. But in this room, they're calling her a hero. City and state attorneys support her. Gardner and her sister prosecutors are part of a new wave who've pledged to make the justice system more fair to people of color. Every prosecutor here has had similar experiences to Kim Reporter: Her complaint says that local authorities have broken a federal law that dates back to the late 1800's and was meant to fight the Ku klux Klan. The lawsuit paints a pattern of racist conduct by some of the officers on the St Louis police force. We have to make sure that the powerful few are not able to manipulate the system. Reporter: In 2016, she won in a landslide. From the start, she says her Progressive approach to criminal justice put her immediately at odds with some on the police force and in the community. I was stopped for having my lights off on Christmas eve while I was delivering Christmas cards to the post office right down the street from my office. I was stopped and held for over 15 min. Just because someone could. And you knew what it was about. We all know what it's about. I don't have to say what it's about. Reporter: Her office has shared with us copies of the hate people have sent her in the mail. The naked racism is too much to read here. And some even threaten her life. For example, "Time to go away forever. If you don't leave something will be done about you. Even if its me." They leave their addresses on the mail to make sure that I know who they are. Reporter: Gardner's lawsuit names her employer, the city of Saint Louis, as well as the head of its police officers association saying that the defendants worked against her to "Thwart and impede her efforts to establish equal treatment under law for all St. Louis citizens at every turn. To remove her from the position to which she was duly elected and perhaps to show her successor what happens to circuit attorneys who dare to stand up for the equal rights of racial minorities in St. Louis." The police officers association of Saint Louis is not taking any of this lightly. Make no mistake, this is the last act of a desperate woman who is simply trying to silence her critics. We will not be silenced. Reporter: The cries for criminal justice reform in this country are now loud and have grown more impatient since the 2014 police shooting death of Michael Brown in Ferguson. The case, just 10 miles from St. Louis, launched a national debate over the policing of black Americans. We're the ground zero that started Ferguson, that has the conversation of the reform efforts that you hear and see around this country. Reporter: After Ferguson, gardener says that inequities of the legal and justice are just no longer acceptable. What are some of the disparities, that unfairness you're talking about that you came to office specifically to tackle? One in three african-amrican men are more likely to go into the criminal justice system. 91% of African Americans are stopped more than any other group. More than 80% of cases and arrests are on af-am men and women; people of color. So why is it that we are represented more than any other group in the criminal justice system? Reporter: As soon as she took office, she dismissed some 30 thousand cases that she said were unprosecutable, which didn't go over well with police. And the relationship wasn't helped with her handling of several officer misconduct cases. In September of 2017 when a white police officer was acquitted in the shooting death of Anthony Lamar Smith. That officer is free. Anthony Lamar Smith is dead. It happens too much. Reporter: St. Louis erupted into protests, and Gardner took a stand with the streets calling for an independent investigation into police misconduct. We believe that the police department cannot investigate themselves. We have to be smart on crime not just tough on crime. It is changing the minds of individuals who have held on to the status quo. Reporter: During the unrest that followed Smith's death, four St. Louis police officers allegedly attacked and beat a black police officer who was working undercover in the middle of the protesters, the officers seen here in this "Usa today" video, were indicted on criminal charges. One of the officers has since pled guilty. Her lawsuit also points to the findings of the plainview project, a report by the non-profit injustice watch which investigated public Facebook posts from police officers across the country. Several of the posts by St. Louis officers suggested they looked forward to harming protesters. One read "Black lives splatter," another depicted a soldier dragging a civilian with the caption "How to handle protesters." And many posts were racist in nature. One, written by an officer who was later fired over his social media use referred to muslims as "Turd goat humpers." While another suggested that March is "Stop blaming white people month." Several of the 22 officers involved were reprimanded or fired. Two officers were fired two were suspended for 16 days or more and four received written reprimands it's not like this went uninvestigated, it's not like it was ignored. Reporter: Gardner didn't stop there. She put many of the officers on an exclusion list, barring them from bringing cases to her office. We decided that that affected their credibility that affected our job. Reporter: Of all her moves, one of her most controversial was her decision to investigate former Missouri governor Eric greitens. Missouri's governor, and a bombshell report alleging he had an extramarital affair and that he threatened the woman into silence. Reporter: Greitens resigned, and the charges against him were dismissed. But an investigator she hired for the case is now charged with perjury and evidence tampering and that's led to the appointment of a special prosecutor who's now investigating her office. It's all just a grand distraction is to distract from the trouble she's in and the trouble is coming. Reporter: Jeffrey Roorda, named in Gardner's suit, underlined today how a judge dismissed a case that Gardner brought against two police officers, citing several hundred instances of prosecutorial misconduct. Roorda also shares that she has to give a deposition tomorrow in that special prosecutor's investigation. Gardner doesn't want to answer for her conduct. That's what this lawsuit is about. You can believe that there are real problems with saint Louis police on race related issues at the same time that you can believe this is a lawsuit that should be dismissed immediately. What do you say to the prosecutors who came down to support to them today? What do you say to those prosecutors who are all black women? I say go home. Your -- your own cities are a disaster because you're conducting yourselves the way Kim Gardner is. Go home. We don't need Kim Gardner, we don't need you, Reporter: Gardner's supporters strongly disagree. Including Boston district attorney Rachael Rollins who joined her today. Do you relate to what she's going through at all? Absolutely. Nobody questioned the discretion of prosecutors when for hundreds of years we were speeding towards mass incarceration. Now that people that are actually from the communities that are over-policed and over-prosecuted are taking these leadership roles and are elected to do so, miraculously people have problems with our prosecutorial discretion. Reporter: This is a fight they say is worth having. And we have good people on the police department but they're stopped by a divisive racial undertone, undercurrent that has taken place in our city, in our police department, the people are tired, want change and are not backing down. Reporter: Our thanks to Steve for that report.
This transcript has been automatically generated and may not be 100% accurate.