Federal prosecutors are opening a civil rights investigation into the shooting death of Stephon Clark, the unarmed 22-year-old who was gunned down in his grandmother’s backyard by police last March.

The announcement by the US attorney’s office and the FBI came hours after the California attorney general, Xavier Becerra, said he wouldnot file criminal charges against the two California police officers identified in the shooting.

“Now that both state and local authorities have completed their investigations into the shooting of Stephon Clark, the US Attorney’s Office and the FBI, in conjunction with the Civil Rights Division of the US Department of Justice, will examine whether the shooting involved violations of Mr Clark’s federal civil rights,” a statement by Sacramento police said. “That examination will involve a review of the substance and results of the state and local investigations, and any additional investigative steps, if warranted.”

Earlier in the day, Becerra had said that a ﻿year-long independent state department of justice investigation had found the officers, Terrence Mercadal and Jared Robinet, believed they were in danger when they shot Clark.

He added that Clark had committed several unlawful acts and had not followed officer commands after being confronted, saying that evidence showed “it was clear he had something in his hand”.

According to an official autopsy, Clark was shot seven times, including three times in the back. An independent autopsy found he was shot eight times.

Five minutes after the two officers fired on Clark they found him face down. Next to his body was a cellphone, which they had mistaken for a firearm.

Tuesday’s developments followed a weekend of protests in Sacramento over the decision by the district attorney, Anne-Marie Schubert, not to press charges against the officers.

In a press conference on Saturday, Schubert described video footage and images from the night of the killing, arguing Clark had turned around and taken up a shooting stance. She also shared personal text messages, phone logs and email drafts from the days leading up to his death. Schubert argued the details were meant to indicate Clark’s state of mind at the time of his death. Family members and advocates, however, described the depiction as a character assassination.

“She used that as a smear campaign or a fake way to justify and condone,” Clark’s mother, Se’Quette Clark, told NPR this weekend. “Her officers weren’t doing – she never once addressed their actions. She presented and painted a picture of my son that was her opinion.”

At a press conference after the district attorney’s announcement, Se’Quette Clark told reporters she was outraged. “They executed my son,” she said. “They executed him in my mama’s backyard. It is not right.”

Schubert’s decision sparked protests in the Sacramento’s affluent Fab 40s neighborhood, trailed by more than a dozen officers on bikes and a line of police vehicles. Police issued 10 orders to disperse, but a wall of riot police at the rear prevented many protesters from returning to their cars.

Near the end of the two-hour march, officers pushed the remaining crowd east and then south onto an overpass, where they kettled the marchers in. More than 80 people were arrested, including religious leaders and journalists covering the march.

9/ Pastor Les Simmons: "What will stop this is justice, is accountability. That is the healing that’s needed." — Nick Miller (@NickMiller510) March 5, 2019

By Tuesday evening, a few dozen demonstrators had gathered outside the Sacramento police headquarters holding signs including “hands up, don’t shoot!”, “Black Lives Matter” and “No justice, no peace, no racist police”, as helicopters hovered overhead.

Meanwhile, advocates are working to change the laws Becerra and Schubert referenced in the evaluation of the departments’ actions.

The California Act to Save Lives legislation, introduced in February, seeks to set clearer limits on police officers’ use of lethal force. The bill is supported by the Sacramento mayor, Darrell Steinberg, as well as organizations including the ACLU and Black Lives Matter.

Becerra said he, too, wanted to work toward preventing deaths like Clark’s from happening in the future.

“A mother lost her son, two young boys lost their father, and two grandparents lost their grandson in their own backyard,” he said, adding that he hoped Clark’s family would work with him to bring about change.

“I hope we can enlist them to be some of the warriors to help us move in the right direction.”