The Los Angeles police commission ruled that officers violated policy when they fatally shot a 30-year-old man in the middle of a mall, a rare official rebuke of deadly force in a city with frequent killings by police.

Police did not follow protocol when they fired shots at Grechario Mack, a 30-year-old father of two, while he was on the ground inside the mall amid a mental health crisis. Mack, who was shot in multiple places including the back, had been holding a kitchen knife and appeared agitated when officers began firing on 10 April 2018.

The commission, a board that reviews police conduct, ruled that the initial shots were in line with policy, but that two officers violated protocol when they fired their final shots at Mack when he was already down. The Guardian chronicled Mack’s killing last year as part of an investigation into law enforcement in Los Angeles county, where hundreds have been killed by on-duty officers or died in custody since 2012, but none of the officers have faced charges.

“It’s a victory,” Quintus Moore, Mack’s father, told the Guardian on Wednesday after the unanimous commission ruling of a violation. “He was down and bleeding and couldn’t move. He was still alive … There was no reason to harm him anymore.”

Mack’s family said the final shots were the ones that killed him. Los Angeles policy dictates that police only use deadly force when someone poses an imminent threat of death or serious injury.

“We want accountability,” Moore said, adding that the commission ruling should lead to criminal charges against the officers. “They should fire them, and they should put them in jail. If they start locking them up and putting them in jail like any other criminal, they will stop doing this.”

The commission has ruled that killings by police were out of policy just a handful of times in recent years, said Melina Abdullah, a Black Lives Matter organizer in Los Angeles who has worked closely with Mack’s family.

Quintus Moore and Catherine Walker, Mack’s parents, seen last year. Photograph: Dan Tuffs/The Guardian

“We were almost in disbelief,” she said, noting that she had tried to prepare the family over the last year for a commission ruling in the officers’ favor, since that is the typical outcome, even in egregious cases. “But how could it be in policy? You murdered this man in the middle of the mall. You stood over him and made sure he was dead.”

The Los Angeles police chief, Michel Moore, previously said he did not believe policies were violated, though his predecessor, Charlie Beck, had said a beanbag shotgun would have been “the most appropriate tool for this”, the Los Angeles Times reported.

The officers said Mack had “displayed pre-fight indicators”, including “moving his head side to side”, and that it appeared he was “preparing for an altercation”, according to the police report. One officer reported that after Mack was hit by an initial round of shots, he fell to the ground, and the knife fell out of his hand. That officer alleged that he then grabbed the knife and tried to get back up, which prompted the lethal shot.

David Winslow, an attorney for the officers, defended their actions in an email to the Guardian on Wednesday, saying it was a “rapidly moving and changing situation that required split-second decision making while trying to protect multiple shoppers from harm”.

The lawyer said the officers attempted to persuade Mack to drop the knife, adding: “Each round they fired was to protect the public, and them, from the threat of deadly harm.”

An employee of a nearby store inside the Baldwin Hills Crenshaw mall, however, previously told the Guardian that she walked right by Mack before the killing and that he did not seem threatening.

Mack’s father said he felt the officers were motivated by racial bias and should have de-escalated the situation without resorting to firing at his son: “They shouldn’t have shot him in the first place.” Mack was probably scared when heavily armed officers arrived on scene, he added: “He was running for his life, he wasn’t running to hurt anyone.”

His family previously described Mack, also known as Chario, as a relative who was fiercely protective of his family, loved to fish, and had graduated high school early as an honor roll student.

“Justice would be Grechario Mack still being alive,” said Abdullah, adding: “This is a step toward accountability … As someone who lives close to the mall, whose kids shop in the mall, I want those officers fired and prosecuted because they are a danger to me and my children and my community.”