A Los Angeles county sheriff’s deputy shot and killed a 27-year-old woman who had called 911 to report that she was under attack by a former boyfriend, police officials and lawyers for the victim’s family said on Thursday. Records show the deputy had killed another person in similar circumstances three years ago.

On 4 December, Niani Finlayson called police and “reported that her boyfriend would not leave her alone and then screaming and sounds of a struggle could be heard”, the LA sheriff’s department (LASD) said in a statement. When deputies arrived at the apartment in Lancaster, a city in the northern region of LA county, they could hear screaming, LASD said.

Finlayson was inside with her nine-year-old daughter and had been injured by her ex-boyfriend and wanted him removed, her family’s attorneys said. The exact circumstances that led to the fatal shooting are unclear and LASD has so far declined to release body-camera footage.

LASD alleged in a statement that Finlayson had a knife and was threatening her boyfriend, at which point deputy Ty Shelton opened fire. The family disputed the police account, saying Finlayson was clearly a victim of domestic violence who needed help and posed no threat to the officers. The coroner said she died from “multiple gunshot wounds”.

Finlayson was a mother of two, and her daughter, Xaisha, witnessed the shooting.

“The police lied that my mom was threatening them,” Xaisha said at a press conference on Thursday alongside her grandparents, calling for Shelton to be prosecuted. “She was my best friend. She was always there for me. It’s unbelievable that she’s gone and she’s not coming back. I miss my mom.” The girl said her two-year-old sister continues to ask where their mother is and she doesn’t know how to respond.

A young Black woman cuddling with a young Black girl, both smiling happily.

Finlayson’s family filed a legal claim against the county and sheriff’s department on Thursday, alleging wrongful death, assault and civil rights violations.

“You have someone who is calling the police for help, and she gets killed by the police who she’s asking for assistance,” said Bradley Gage, the family’s attorney. “If you call police for help, you think the officers are going to protect and serve you. You don’t expect them to hunt and kill you.”

LASD said in a statement Thursday it had not officially received the family’s claim, but would be releasing body-camera footage by next week. The inspector general’s office would conduct a “robust review process … where every aspect of the shooting is thoroughly examined and evaluated to see if department policies and procedures were followed”, and the LA district attorney’s office would determine whether the shooting was legally justified, the statement said, adding: “The department is deeply committed to protecting our diverse communities without bias and prejudice.”

Shelton could not be reached and the sheriff’s deputy union did not immediately respond to an inquiry.

Previously, Shelton killed Michael Thomas, 61, on 11 June 2020 in a similar case. Shelton had been responding to a potential domestic violence call and when the deputies arrived, they demanded he open the door, officials said. Thomas’s girlfriend later said she had been having a verbal argument with Thomas, who had been unarmed, and that he had tried to stop the officers from entering, citing the fourth amendment. Thomas had also been afraid police would shoot him, his family said, and officials later confirmed Thomas had said: “I am now in fear for my life. You guys … just killed somebody.”

Shelton fatally shot Thomas in the chest. The killing was not captured on camera. The case was one in a series of LASD killings that summer that caused widespread protests, and prosecutors declined to file charges against Shelton. LASD did not respond to questions about Shelton’s previous killing.

Finlayson’s mother, Tracie Hall, said her daughter had been working to become a nurse and an in-home care service worker, designed her own clothes and wanted to make a phone app for children. “I’m going to miss my daughter braiding my hair, the simple things. It’s so unfair,” she said, adding: “I hope Ty Shelton looks himself in the mirror and says: ‘I have destroyed another life for no reason.’ [He] put my granddaughter in so much danger.”

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“He should not be allowed to roam free and continue to have a job and provide for his family, because my daughter is not here to provide for her family,” she said.

Finlayson’s father, Lamont Finlayson, said she had recently moved into the apartment and was excited to celebrate her first holidays there: “It just breaks me to my bone. I can’t eat, I can’t sleep, I can’t walk … they didn’t tase her, mace her, baton her or beanbag her. They just shot her like a dog in her own place … and taken so much away from us.”

Myesha Lopez, Thomas’s daughter, said on Thursday that she was furious, but not surprised to learn that Shelton had fatally shot another person: “He’s been given a license to kill … and again he violated someone’s civil rights by going to their home and murdering them.” She said it was particularly upsetting considering how she and others had protested and warned that Shelton was dangerous: “It is the fruition of my greatest fear – that someone else would relive what I experienced.”

Local advocates in the Antelope Valley region in northern LA county have called for Shelton to be fired and charged.

“We want him out of there and prosecuted and not just moved to another county to stay in law enforcement,” said Waunette Cullors, a co-founder of Cancel the Contract, a group that is assisting the family and that organizes against police brutality in the area. “There is no accountability. The sheriff keeps finding excuses to validate murdering us.”

The sheriff’s department has repeatedly been accused of using brutal force against Black women in the region. In June, a deputy was caught on camera throwing a woman to the ground outside a Lancaster grocery store and placing his knee on top of her. The woman had been recording a police encounter. LASD also released footage in July of an encounter in Palmdale, a neighboring city, in which a deputy was seen punching a woman twice in the face as she held her newborn baby.

“Sheriffs are running rampant in Antelope Valley and are allowed to harm Black women especially and nothing is happening,” said Cullors. “Everyone considers it to be a norm.”