Benjamin Crump is a civil rights attorney and advocate known for his work representing the families of Trayvon Martin, Michael Brown, Danny Ray Thomas and others, and is the founder and principal of Ben Crump Law. The opinions expressed in this commentary are his own.

(CNN) If you are mentally ill and black, you already have two strikes against you if you come into contact with law enforcement. In fact, one in four victims of a police shooting have signs of mental illness, according to The Washington Post's police shooting database . And the unrelenting spate of police shootings of unarmed black men that dominates the national news demonstrates the dangers of being black.

Police officers shot and killed Saheed Vassel, a black man well known (even among police) as someone who lived with mental illness, on a Brooklyn street corner when they mistook a metal pipe that he was holding for a gun. Days before the shooting came, a new US Supreme Court decision was made that stunned civil rights advocates and revealed a third strike: the unwillingness of our justice system to hold police accountable.

The court ruled in favor of an Arizona officer who shot a woman with a history of mental illness.

Justice Sonia Sotomayor wrote in a dissent that the court's recent decision was not only wrong, but it tells law enforcement that officers "can shoot first and think later, and it tells the public that palpably unreasonable conduct will go unpunished.''

Sotomayor, who was joined in the dissent by Justice Ruth Bader Ginsburg, warned that the doctrine of limited immunity for police is being used as "an absolute shield for law enforcement officers.''

She's right. I see that shield allowing more and more officers who use excessive and often deadly force -- especially on unarmed people of color and those with a mental illness -- to get away with murder.

In the Arizona case, an officer shot victim Amy Hughes four times when she refused to drop a kitchen knife. The officer said he shot Hughes because he thought she posed a threat to her roommate. Later, the roommate said that Hughes had a history of mental illness and that she didn't feel concerned for her own safety. In fact, as the New York Times reported, Hughes "was not moving, spoke calmly, held the knife at her side and made no aggressive movements."

Hughes, who survived and was not charged with any crime, filed a lawsuit against the officer for shooting her.

As her case made its way through the courts, the US Court of Appeals for the Ninth Circuit ruled in favor of Hughes, overturning an earlier district court's summary judgment in favor of the officer. The Ninth Circuit Court of Appeals held that there were real questions of fact, such as whether Hughes had presented a real threat and whether the officer had given adequate warning before shooting.

But the Supreme Court sided with the officer, shielding him from the lawsuit. The court said the officer believed Hughes was a threat to her roommate and had "mere seconds to assess the potential danger." The justices -- without briefing or oral argument -- overturned the appeals court ruling.

JUST WATCHED Hill: Police didn't seem to follow procedures Replay More Videos ... MUST WATCH Hill: Police didn't seem to follow procedures 02:31

Could it be that the justice system's apathy toward holding police officers accountable for their actions is empowering police to shoot first without thinking -- just as Sotomayor said in her dissent?

In the case of the late Vassel in Brooklyn, witnesses told the New York Times that the officers appeared to shoot almost immediately after arriving at the street corner where Vassel was standing.

In Houston, Danny Ray Thomas, an unarmed black man who was clearly in mental distress, was shot and killed when a Harris County deputy sheriff arrived at a busy intersection where Thomas was walking with his pants down.

According to his relatives, Thomas suffered from depression -- two of his children were murdered in 2016. His family said he wasn't a bad man, just deeply troubled.

The community is left to wonder: Couldn't law enforcement have found a less violent, more humane way to intervene rather than killing a man who even the sheriff said was "obviously in a state of crisis of some kind?"

But because he was black, the odds were stacked against him. The Washington Post's ongoing tally of police-involved shootings shows that officers have killed 57 people known to suffer from mental illness so far this year. Of those, 31 (54%) were white and 11 (19%) were black. Yet the US census shows whites make up 77% of the population, and blacks make up just 13%.

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The color of one's skin and the state of one's psyche should not be compounding risk factors. And when police make mistakes based on those factors, our institutions of justice have a moral obligation to stand up for the diverse and vulnerable people who make up our country.