It's Very Difficult to Convict Officers in Police Shootings, Experts Say
In this image made from July 6, 2016, video captured by a camera in the squad car of St. Anthony Police officer Jeronimo Yanez, the Minnesota police officer shoots at Philando Castile in the vehicle during a traffic stop in Falcon Heights, Minn. AP
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A pair of court cases laid the foundation. The U.S. Supreme Court, in Tennessee v. Garner in 1985, ruled that an officer can use deadly force against a fleeing suspect if they believe they are in danger of death or serious physical harm.
Four years later, the Supreme Court ruled in Graham v. Connor that officers who use force must be judged on a standard of "objective reasonableness."
"For better or worse, whether you believe in it or not, [the law] is very favorable to police use of force," Harris said. "That objective standard is very wide in terms of giving police discretion."
Tensing, Yanez and Heaggan-Brown all said they feared for their life during their fatal encounters, all of which were captured on camera, sparked protests, and reignited national fury over police brutality.
Many civil rights advocates and plaintiffs attorneys say the laws governing use of force give the police far too much latitude to claim they feared for their lives.
Police often "conjure up something in their mind that's not a real danger," said attorney Benjamin Crump, who has represented the families of Trayvon Martin and Michael Brown.
Two of the high-profile recent cases hinged on questions of reasonable fear:
Tensing, the Cincinnati officer, said he feared DuBose, the motorist he pulled over for a missing front license plate, would use his car to kill him. Prosecutors said the car was not moving until about one second before Tensing shot DuBose.
Yanez, the former St. Anthony, Minnesota, officer, testified that Castile, the cafeteria worker he pulled over, ignored the officer's commands not to pull out his gun. Castile, who had a permit for his weapon, had told Yanez he was armed. In squad-car video of the shooting, Castile can be heard saying, "I'm not pulling it out" and, right before he died, "I wasn't reaching..."
In the last 12 years, 82 state and local police officers have been charged with murder or manslaughter in an on-duty shooting, according to data compiled by Stinson, the Bowling Green associate professor, who tracks police crime.
Of those officers charged since 2005, the year Stinson began collecting data, 29 were convicted and 34 were not.
The wider social issue, according to Crump and other civil rights advocates, is implicit racial bias — the idea that every person holds subconscious prejudices — even those in positions of supposed impartiality, such as judges.
"We need to look at implicit racial bias as an issue not just for officers [involved in on-duty shootings] but for jurors, too," said Kami Chavis, the director of a criminal justice program at Wake Forest University School of Law.
DuBose, Castile and Smith were black; Tensing is white, Yanez is Latino and Heaggan-Brown is black.
What's more, some jurors come to court with a "dominant narrative that says police are the good guys," Harris said.
"We know that's not always true, of course," Harris added. "But persuading jurors that the police have committed a crime, and not just made a mistake, goes against that narrative. It's a very steep hill for prosecutors to climb."
Daniel Arkin is a reporter for NBC News.
Ron Allen is an NBC News correspondent based in New York.