Freddie Gray died in Baltimore police custody. The justice system will punish no one for it.

More than a year ago, Baltimore police officers arrested Freddie Gray, put him in a van while he was cuffed but without a seat belt, and let him thrash around the back of the vehicle until he broke his spine — an injury that would later kill him.

On Wednesday, it became clear that the criminal justice system will punish no one for Gray’s death: Prosecutors announced that they will drop all remaining charges against the six police officers involved, after three of the officers were acquitted of all charges in court.

In a searing statement, Baltimore state’s attorney Marilyn Mosby explained the decision to drop all remaining charges:

After much thought and prayer, it has become clear that without being able to work with an independent investigatory agency from the very start, without having a say in the election of whether cases proceed in front of a judge or jury, without communal oversight of police in this community, without substantive reforms to the current criminal justice system, we could try this case 100 times just like it and we would still end up with the same result.

The decision is an enormous loss for Black Lives Matter activists who have demanded justice for Gray, who was black. After protests and even riots plagued Baltimore more than a year ago, it’s clear that those voices demanding someone at the Baltimore Police Department pay will not be heard.

More broadly, the case shows just how difficult it is to prosecute police, even when the victim’s death was deemed a homicide by the state medical examiner. For activists, this difficulty in landing successful prosecutions is one of the reasons that Black Lives Matter exists in the first place: The fact cops aren’t always punished for wrongdoing, especially when a black victim is involved, proves to many that black lives really aren’t valued in America.

The truth is it was always a long shot that any of the officers involved in Gray’s death would go to prison. Legal observers had long warned that the charges against police would be very hard to prove in court. But compounding that problem is the fact that it’s notoriously difficult to prosecute police officers in America.

Police are very rarely prosecuted for killings — and not just because the law allows them wide latitude to use force on the job. Sometimes the investigations fall onto the same police department the officer is from, which creates major conflicts of interest. Other times the only available evidence comes from eyewitnesses, who may not be as trustworthy in the public eye as a police officer.

In the Gray case, there was no video of Gray’s experience in the police van or the many times he was stopped — only video of his initial arrest. So even though the evidence suggests that Gray wasn’t wearing a seat belt in a moving vehicle, cried for medical care, and former Baltimore Police Commissioner Anthony Batts admitted that officers wrongly ignored Gray’s cries for help, the lack of video evidence makes it all the more difficult to prove that an individual police officer or six of them were culpable for the death.

“There is a tendency to believe an officer over a civilian, in terms of credibility,” David Rudovsky, a civil rights lawyer who co-wrote Prosecuting Misconduct: Law and Litigation, told Amanda Taub for Vox. “And when an officer is on trial, reasonable doubt has a lot of bite. A prosecutor needs a very strong case before a jury will say that somebody who we generally trust to protect us has so seriously crossed the line as to be subject to a conviction.”

This fits a pattern in Maryland, where Baltimore is located. An analysis from the American Civil Liberties Union of Maryland found that police were charged in less than 2 percent of police-involved killings between 2010 and 2014. In these killings, 69 percent of the victims were black, even though they make up 29 percent of Maryland’s population. About 41 percent of the victims were unarmed.

If police are charged, they’re very rarely convicted. The National Police Misconduct Reporting Project analyzed 3,238 criminal cases against police officers from April 2009 through December 2010. They found 33 percent were convicted, and only 36 percent of those officers ended up serving prison sentences. Both of those figures are about half the rate at which members of the public are convicted or incarcerated.

The result is a justice system that many believe lets police officers act recklessly and even maliciously and get away with it. For Black Lives Matter activists in particular, it suggests that police officers can nearly indiscriminately kill black people — evidence, they think, that black lives don’t matter.