The justices, in a 9-0 ruling authored by liberal Justice Elena Kagan, threw out a lower court's dismissal of the lawsuit by Janice Hughes accusing the officer, Roberto Felix Jr., of violating the U.S. Constitution's Fourth Amendment prohibition on unreasonable searches and seizures by using deadly force against her son. Ashtian Barnes, 24, was killed in the 2016 incident.
The justices decided that the lower courts had impermissibly limited their review of the officer's actions leading up to the shooting.
"Today, we reject that approach as improperly narrowing the requisite Fourth Amendment analysis," Kagan wrote.
"To assess whether an officer acted reasonably in using force, a court must consider all the relevant circumstances, including facts and events leading up to the climactic moment," Kagan added.
The case tested whether lower courts should analyze police conduct by considering only the exact "moment of threat" to the officer, while excluding the officer's actions prior to the deadly episode - even by a few seconds.
Lower courts found that Felix's actions were reasonable, as they considered only the two seconds before the officer fired his first shot, when he was hanging onto the moving vehicle and believed his life was in danger.
The "moment of threat" doctrine is used by courts in several regions of the country, including the Texas federal courts overseen by the New Orleans-based 5th U.S. Circuit Court of Appeals, where this case was decided - but not in other federal courts, according to lawyers for Hughes.
Hughes sued the officer and Harris County, seeking monetary damages. A trial judge and then the 5th Circuit ruled against Hughes.
Felix, a Harris County Constable's Office traffic enforcement officer, pulled Barnes over on April 28, 2016, because the rented Toyota Corolla he was driving on a Houston highway had outstanding toll violations.
Barnes searched for his license and proof of insurance, and suggested they might be in the trunk, according to court papers. Felix claimed to smell marijuana, though no evidence of drugs was found in the car, the filings showed.
Felix ordered Barnes out of the vehicle, but instead the car began to move forward, according to court papers. Felix stepped on to the driver's door sill and shouted at Barnes not to move, then fired twice, the filings showed. Barnes died at the scene.
Local officials investigated the shooting but Felix was never charged with a crime. An internal police probe also cleared Felix of any wrongdoing, according to court papers.
The lawsuit alleged that the shooting resulted from Felix's dangerous decision "to pull his gun without provocation, then point that gun in Ashtian Barnes' direction, then leaping onto a moving vehicle and firing twice into it without warning, with no clue as to what he was aiming at."
Lawyers for Felix had argued against a ruling that would make it harder for police to defend their use of force - even if an officer made a mistake, used bad tactics or had poor planning.
During arguments before the Supreme Court in January, the justices seemed skeptical of the "moment of threat" doctrine, while some worried that a ruling against Felix would deter police from doing their jobs.
Conservative Justice Neil Gorsuch noted during the arguments that, even if courts may look at the totality of the circumstances of an incident involving police, officers are still protected by a powerful legal defense called qualified immunity.
