Reprinted with permission from AlterNet.

To the dismay of Black Lives Matter activists and criminal justice advocates, juries often decline to convict police officers for excessive use of force.

St. Anthony police officer Jeronimo Yanez is one such example. In June, a jury acquitted Yanez of all charges including second-degree manslaughter for the fatal shooting of Philando Castile during a failed traffic stop last year. His acquittal reflects a larger trend in which officers are rarely held accountable during police violence cases. A New York Times analysis of 15 high-profile cases found that only two resulted in a conviction or guilty plea.

There are numerous systemic barriers that historically hinder police accountability. Statutes found in police union contracts and police bills of rights, for instance, often protect officers at the expense of holding them accountable for their actions. But perhaps one of the strongest barriers to police accountability is enshrined in two precedent-setting Supreme Court cases.

In 1985, the Supreme Court heard the case Tennessee v. Garner, in which a Memphis police officer shot an unarmed teenager following a house burglary. The court evaluated whether the officer’s deadly use of force was a violation of the Fourth Amendment right against unlawful search and seizure.

The Supreme Court concluded in Tennessee v. Garner that an officer’s use of deadly force must be based on probable cause and should be reasonable.

“Where the officer has probable cause to believe that the suspect poses a threat of serious physical harm, either to the officer or to others, it is not constitutionally unreasonable to prevent escape by using deadly force,” the court wrote in its opinion.

Davis Harris, a professor of law at the University of Pittsburgh who specializes in police issues and the host of the podcast Criminal (In)justice, calls the use of deadly force the “ultimate seizure.”

The reasonableness standard was further defined in the 1989 Supreme Court case Graham v. Connor, in which a physical altercation took place between a man having an insulin reaction and police officers who assumed the man was drunk and attempted to arrest him. Here the Supreme Court established that the “reasonableness” of an officer’s use of force must be judged through the perspective of a “reasonable officer on the scene” and must take into account the fact that “officers are forced to make split-second decisions about the amount of force necessary in a particular situation.”

“I think as a legal standard it is so open and so favorable to police that it’s a big part of the reason we get the results that we do when a case goes to trial,” Harris noted.

Because of the objective reasonableness standard established in Graham v. Connor, jurors such as the ones in the Yanez case are asked to evaluate an officer’s actions based on the particular circumstances of the case. External factors like a police department’s policies are not taken into account.

In an interview with Minnesota Public Radio following Yanez’s acquittal, an anonymous juror said the jury was at first too nitpicky in analyzing Yanez’s interaction with Castile, leading to a deadlock in the first week of deliberations.

“One of the things they told us we couldn’t take into account was this hindsight 20/20,” the juror told MPR. “And that’s what a lot of us, some of us, kept doing. We kept saying an officer’s training or what we would do in the situation, and you know, nobody really knows how a human is gonna react.”

The openness of objective reasonableness allows defense teams to craft an argument that attempts to justify the officer’s actions and sway the jury in his favor. In his testimony, Yanez said the smell of marijuana made him fear for his life—a defense that has commonly been employed by other officers in a criminal case. Harris said this type of fear defense is often successful in fulfilling the objectively reasonable standard and can convince juries to give the officer the benefit of the doubt.

“This isn’t for us to second-guess in the sense that we would see it through our own eyes,” Harris said. “We look at it through the eyes of the police officer in the fast-moving and dangerous circumstances in which he or she may find themselves.”

Another factor influencing jurors’ general deferment to police under the objective reasonableness standard is the public’s overall positive outlook on law enforcement. Surveys conducted by Gallup and the Pew Research Center in 2016 show that Americans have an overall positive outlook on police. Harris said it can be difficult for jurors to contradict the long-held perception that officers are to be respected and trusted.

“They’re going to see police officers as people who try to help, who try to protect, who do their best in a terribly risky situation,” he said. “If you’re asking a jury to convict a police officer, you’re taking that narrative and flipping it on its head.”

However, a breakdown of race reveals a wide perception gap between whites and blacks on law enforcement. The same 2016 Pew study found that black people do not think as highly of police as white people do; 33 percent of blacks believe the police always use the right amount of force in each situation, compared to 75 percent of whites.

These disparities in perception can trickle down into the courtroom and could impact the outcome of a criminal case involving lethal use of force, but only if white people and black people are proportionally represented in jury pools. This was not the case in Yanez’s trial (the 15-person jury was made up of 13 white jurors and only two people of color) and it is not the case for trials involving officer use of force writ large.

Further analysis from the Huffington Post of 13 trials involving police shootings between August 2014 and December 2016 found that “majority-white juries decided 11 of those 13 cases.” Three of those 11 majority-white juries returned not-guilty verdicts, and another four resulted in mistrials due to a hung jury. The Huffington Post also found that the racial makeup of the jury was not reflective of the local community’s demographics, potentially tilting the jury’s decision-making process more to one side than the other.

While the objective reasonableness standard has remained the precedent for evaluating officer use of force since 1989, the public scrutiny of police violence incidents has only grown, with more incidents garnering national media attention. But if criminal justice and police reform advocates want to change the standard by which officers are judged in court, one formidable obstacle stands in their way: the Supreme Court. Even Harris is doubtful that the standard could be changed, noting that the Supreme Court has generally been protective of police regardless of the court’s ideological makeup.

“I say that because the makeup of the Supreme Court is basically status quo in terms of where the votes are for what kinds of positions are on these issues,” Harris said. “For the last 10 years it really hasn’t changed all that much, and now with the Gorsuch confirmation, it really kind of stays the same.”

So far this year, 581 people have been shot and killed by law enforcement, according to the Washington Post’s database. Should any of the officers involved in those incidents be brought to trial, the objective reasonableness standard will undoubtedly play a role in how they are judged. If that standard ultimately influences the jury to acquit the officer, it will inevitably reveal the divide between those who support police and those who want accountability.

“Obviously when you have the law that is clearly tilted in one direction,” Harris said, “you’re not always going to get something that looks like justice to everyone.”