George Floyd’s death last May set off a ripple effect that spread across the globe, culminating in mass protests, cultural and political reckonings on race, and, on Tuesday, a rare conviction for the officer who killed him.

Bringing criminal charges and securing convictions against officers is notoriously difficult. From 2005 through June 2019, 20 out of 104 police officers charged with murder or manslaughter for on-duty shootings in the U.S. were convicted through a jury trial, according to a study from Bowling Green State University.

After a three-week trial, it took a jury about 10 hours to reach the unanimous decision to convict former Minneapolis police officer Derek Chauvin of all three charges against him, including second degree murder.

The prosecution’s case rested on a rare confluence of strong video evidence and damning testimony, including from the Minneapolis chief of police and a number of eyewitnesses.

In the aftermath of the verdict loom familiar questions about what it means and what comes next. Several criminal justice experts, including a former federal prosecutor and a former police chief, talked to the PBS NewsHour about what made this case stand out and what they see as the necessary steps toward greater accountability.

The video

The 9-minute and 29-second video of Chauvin pressing his knee into Floyd’s neck became a signature piece of evidence in the trial.

In police-involved killings where there is video evidence, the footage is often blurry, showing frantic or quick movements, or an obstructed view, said Andrea Headley, an assistant professor who specializes in criminal justice policy at Georgetown University.

During the 2016 police shooting of Philando Castile in Minnesota, for instance, grainy police dash cam video captured Castile handing over his license to officer Jeronimo Yanez through his car window before saying, “Sir, I have to tell you, I do have a firearm on me.” Yanez is then heard warning Castile not to reach for the gun, before firing multiple shots in the car where Castile’s girlfriend, Diamond Reynolds, and her four-year-old daughter were passengers. Castile’s actions leading up to the shooting were out of view, and ultimately, a jury acquitted Yanez of all charges.

MORE: New federal action and greater calls for change follow Chauvin trial, conviction

In Chauvin’s case, the principle video shot by a 17-year-old bystander was clear and relatively still. “It was almost like someone’s watching a movie,” Headley said, speaking to the quality of the bystander video. “I think having that video evidence in such a clear, distinct way, where you can see the vivid act of George Floyd losing his life slowly happening over time … that evidence in and of itself is compelling.”

Floyd can be seen telling the officers he can’t breathe and calling out for his mother.

“It was so long, so painful. … I think that was super significant. It was a grisly death in a vicious time, during a pandemic,” said Lenese Herbert, a former federal prosecutor who teaches criminal law and procedure at Howard University.

During the trial, prosecutors also showed video from police body cameras that allowed jurors to see multiple perspectives of Floyd’s murder, said Carol Archbold, professor of criminal justice at North Dakota State University. The video from officers Thomas Lane, J. Alexander Kueng and Tou Thao, who have also been charged in Floyd’s killing, showed the officers struggling to get handcuffed Floyd into a police car. Later, when Floyd is on the ground, the video showed Lane asking Chauvin twice whether they should roll Floyd on his side. Chauvin, whose knee was on Floyd, said no. At another point, Kueng can be seen checking Floyd for a pulse and telling Chauvin he cannot feel one, but Chauvin’s knee remains on Floyd’s neck.

The prosecution team

Experts said the prosecution used the video footage and witness testimony effectively during the trial.

Even with the amount of video, the odds were still stacked against the prosecution given the low conviction rates for officers, said Hassan Aden, former chief of police for the Greenville Police Department in North Carolina who has served as a monitor for court agreements with police departments that mandate reforms.

The prosecution had an “all-star” team of lawyers, Aden said, led by Minnesota Attorney General Keith Ellison, who did not speak in court. Ellison, a civil rights attorney prior to becoming attorney general, assembled a group of local prosecutors and outside attorneys to work on the case.

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The prosecution’s case reflected an intentional use of video and a range of witnesses to lay out the timeline and the facts, Aden said. This includes highlighting how Chauvin’s actions in the video departed from the Minneapolis Police Department’s policies and training.

One point of criticism throughout the trial that Herbert believes helped prosecutors is the invocation of the “Minnesota Nice” demeanor when questioning witnesses or challenging the defense. That cultural attitude of niceness in Minnesota has been accused of perpetuating a dismissal of racism in the community. But in this case, Herbert said it may have helped the prosecution connect with the jury.

“The kind of prosecution and defense that is OK in some jurisdictions like the District of Columbia, for example, that’s much more aggressive, much more in-your-face … does not go over well in jurisdictions where the notion of politeness and gentleness and kindness are more significant,” Herbert said.

The witnesses

Prosecutors presented a range of testimony, including emotional eye witnesses, first responders, medical experts and current members of the Minneapolis Police Department.

The defense team also called eye witnesses and medical experts in its attempt to claim that Floyd resisted arrest and that carbon monoxide exposure, a tumor in Floyd’s lower abdomen and fentanyl and methamphetamine in his system contributed to his death.

At one point, the defense called Minneapolis Park Police officer Peter Chang, who responded to the scene during Floyd’s arrest. He testified that the crowd grew “more loud and aggressive” toward officers, saying that he was concerned for their safety.

“The defense tried to make some of the bystanders almost be responsible for the situation,” Archbold said. “I think that the prosecution did a really good job being able to show the video and you can hear the desperation in the voices of the people who are standing there watching this occur.”

MORE: How the Chauvin verdict could become a ‘defining moment’ for future policing

Charles McMillian, a 61-year-old eyewitness, began to cry on the stand while watching video of the incident, telling the court “I feel helpless.”

Perhaps most significant for prosecutors was testimony from Minneapolis police chief Medaria Arradondo, the department’s medical training coordinator Officer Nicole Mackenzie, and Sgt. Jody Stiger, a use of force expert with the Los Angeles Police Department.

Arradondo said Chauvin violated policy in kneeling on Floyd’s neck, offering a rare public condemnation by a police chief of his own officer.

“Once Mr. Floyd had stopped resisting, and certainly once he was in distress and trying to verbalize that, that should have stopped,” Arradondo said during the trial.

Deborah Ramirez, a law professor with Northeastern University, said testimony of officers against one of their own is “incredibly rare.”

“[Arradondo] crossed the blue line and walked into that courtroom and told the jury … ‘this is not what we’re trained to do,’ and then went through explicitly what [Chauvin] should have done and what he didn’t do.”

The future for police accountability

Criminal justice experts noted the significance of the Chauvin trial verdict, both in terms of the difficulty in prosecuting police and what this outcome means for the families of victims and members of communities that are disproportionately affected by police use of force.

“I think that the world can breathe now, because they all stood behind George through a pandemic, through COVID marching. And justice for George means freedom for all,” Floyd’s brother Philonise Floyd told PBS NewsHour correspondent Yamiche Alcindor the day after Chauvin’s conviction.

On Wednesday, U.S. Attorney General Merrick Garland announced an investigation into the policies and practices of the Minneapolis Police Department.

When it comes to addressing police use of force on a systemic level, government officials and law enforcement agencies need to be less reactive and more focused on “preventing and detecting these incidents before they occur,” Ramirez said.

READ MORE: Democrats’ police reform bill faces opposition in the Senate — but that’s only the first hurdle

Headley described the prosecution of officers as an important “back-end” mechanism for police accountability, but emphasized the need for front-end solutions that will prevent unnecessary violence in the first place. Proposals for those solutions are highly debated and vary widely. Some activists want to dismantle and rebuild police departments. Others want to reallocate police funding for non-law enforcement services.

Ramirez supports mandating that officers hold professional liability insurance, that would rise in cost when officers engage in malpractice like using excessive force. Herbert said the Supreme Court can play a role by weighing in on the qualified immunity doctrine it created that legally protects public officials like police officers when performing discretionary functions of their jobs.

Headley said federal legislation and guidance will be important given the country’s fragmented policing system, comprising more than 18,000 departments. The Democratic-controlled House passed a major policing reform bill in March known as the George Floyd Justice in Policing Act. The bill would lower the legal standard required to convict an officer for misconduct, establish a national database to track police misconduct and provide grants to help states conduct investigations into alleged constitutional abuses by law enforcement. It has not received a vote in the Senate.

Experts said the nationwide conversations and protests sparked by Floyd’s murder may keep criminal justice solutions at the forefront of people’s minds.

“There’s a lot of work to be done,” Archbold said. “I think that really requiring our government to step in and make real sweeping changes is the only way that we’re going to see a change. Because what we’ve been doing is not working.”