This article is more than 2 years old

This article is more than 2 years old

The family of an unarmed black man whose trousers were around his ankles when he was shot dead by a Texas police officer has filed a wrongful death lawsuit.

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The federal civil action alleges that the Harris county sheriff’s office has a pattern of shooting suspects who do not pose a physical threat and are experiencing a mental health crisis.

Danny Ray Thomas, 35, was killed by deputy Cameron Brewer in a north Houston street at about 1pm on 22 March. The case against Brewer and the county seeks damages and claims the officer used excessive force “even after observing that Mr Thomas was unarmed and clearly in a state of crisis or suffering from mental health problems, and was not then presenting any objective danger to others or himself”.

Police dashcam footage and a cellphone recording from a bystander show Thomas in a minor altercation with another man. Thomas then walks towards Brewer, who backpedals and yells: “I’ll shoot your ass, man, get down, man!”

Danny Ray Thomas with his son Damari. Photograph: Marketta Thomas

The moment that the 44-year-old fires a single shot into Thomas’s chest is not captured on video, but happens less than 30 seconds after Brewer arrives. His body camera, issued that day, was left charging in his vehicle.

“If you’re mentally ill and you’re black then you already have two strikes against you when you encounter law enforcement,” Benjamin Crump, a civil rights attorney, told a news conference on Thursday. “My God, he had his pants down by his ankles. All you have to do is push him, not give him a bullet to the chest.”

Crump is also representing the family of Stephon Clark, an unarmed 22-year-old whose killing in his grandmother’s back yard by police in Sacramento last month set off a wave of protests in the Californian capital.

Bob Hilliard, another of the Thomas family’s lawyers, said footage showed Brewer, who is black, putting his knee into the back of Thomas’s lifeless body and handcuffing him. Brewer was equipped with a stun gun, baton and pepper spray but did not use them, according to the court filing.

Thomas’s death is under investigation by the sheriff’s office and the Houston police department. Evidence is expected to be reviewed by the Harris county district attorney’s office and presented to a grand jury, which will decide whether to indict the officer on criminal charges.

Ed Gonzalez, the Harris county sheriff, said last month Thomas was “foaming at the mouth” and “obviously in a state of crisis of some kind” and expressed concern that the officer went straight to lethal force rather than attempting to de-escalate the situation. The sheriff pledged a transparent and thorough investigation.

On Thursday, Thomas’s sister, Marketta, wore a T-shirt with a photograph of her older brother and wept as she recalled the trauma caused by the death of two of his children, who were allegedly drowned in a bathtub by their mother in 2016.

Facebook Twitter Pinterest An attorney for the family, Ben Crump, announces the lawsuit outside the court. Photograph: Jason Risner

“I lost my best friend,” she said. “No one with mental illness … deserves to die”.

Crump said the incident underlines the need for better training of police and greater accountability. He recalled the fatal shooting of Terence Crutcher, a black man walking with his hands up, in Tulsa, Oklahoma, in 2016. Crutcher’s family have filed a wrongful death lawsuit. The officer who shot him was acquitted of manslaughter.

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According to a Guardian investigation, The Counted, 27% of people killed by US police in the first five months of 2015 had mental health problems.

Still, criminal convictions of officers who use deadly force are rare. In 2012 an officer with the Houston police department fatally shot Brian Claunch, a mentally ill double amputee in a wheelchair who was holding a pen when police responded to a disturbance call at his care home.

The officer was cleared by a grand jury and an internal investigation.