IRVINE, Calif. — LAST week, a grand jury was convened in St. Louis County, Mo., to examine the evidence against the police officer who killed Michael Brown, an unarmed black teenager, and to determine if he should be indicted. Attorney General Eric H. Holder Jr. even showed up to announce a separate federal investigation, and to promise that justice would be done. But if the conclusion is that the officer, Darren Wilson, acted improperly, the ability to hold him or Ferguson, Mo., accountable will be severely restricted by none other than the United States Supreme Court.

In recent years, the court has made it very difficult, and often impossible, to hold police officers and the governments that employ them accountable for civil rights violations. This undermines the ability to deter illegal police behavior and leaves victims without compensation. When the police kill or injure innocent people, the victims rarely have recourse.

The most recent court ruling that favored the police was Plumhoff v. Rickard, decided on May 27, which found that even egregious police conduct is not “excessive force” in violation of the Constitution. Police officers in West Memphis, Ark., pulled over a white Honda Accord because the car had only one operating headlight. Rather than comply with an officer’s request to get out of the car, the driver made the unfortunate decision to speed away. The police chased the car for more than five minutes, reaching speeds of over 100 miles per hour. Eventually, officers fired 15 shots into the car, killing both the driver and a passenger.

The Supreme Court reversed the decision of the Court of Appeals for the Sixth Circuit and ruled unanimously in favor of the police. Justice Samuel A. Alito Jr. said that the driver’s conduct posed a “grave public safety risk” and that the police were justified in shooting at the car to stop it. The court said it “stands to reason that, if police officers are justified in firing at a suspect in order to end a severe threat to public safety, the officers need not stop shooting until the threat has ended.”