Marking the 1-year anniversary of Stephon Clark's death in Sacramento

The Reverend Al Sharpton, civil rights activists and family members on Monday commemorated the one-year anniversary of the shooting death of Stephon Clark by Sacramento police.

"This case is a national disgrace," Sharpton said on the steps of the California State Capitol. "That police have the right based on their imagination to use deadly force. That all you have to do is say 'I thought it was a gun.' Anyone who doesn't know the difference between someone on a cell phone and someone with a gun shouldn't be on the force."

Clark, a 22-year-old black man, was unarmed when he was gunned down in his grandmother's back yard by officers on March 18, 2018. Two Sacramento police officers who killed him said they thought he had a gun because they saw a flash of light in his hands. It turned out, he had been holding a cell phone.

Added civil rights attorney Ben Crump: "What is going on in California? What is going on in America? There are two forms of justice in this country."

Disputing claims that Clark might have wanted to be shot, Crump said: "He wasn't trying to commit suicide by cop. He was trying to get home!"

WATCH: One-year anniversary of the killing of Stephon Clark

Crump said he is supporting a bill first introduced after Clark's slaying that would make California the first state to allow police to use deadly force only when it's necessary to prevent imminent and serious injury or death and if there's no reasonable alternative, such as warnings, verbal persuasion or other methods.

It's not clear the measure will pass this year, particularly because police associations are offering a less sweeping alternative that would keep the current legal standard but calls for more training and an emphasis on trying to calm suspects.

Weeks of protests have swept through California's capital city after state Attorney General Xavier Becerra and Sacramento County District Attorney Anne Marie Schubert separately announced that neither officer would be charged with a crime. Schubert also disclosed of text messages between Clark and the mother of his children, who had filed a domestic violence complaint against him two days leading up to his shooting. Schubert also disclosed toxicology results showing traces of cocaine and other drugs in Clark's system.

On Monday, Sequette Clark, Stephon Clark's mother, said what the DA did was "unnecessarily rude and defamed his character."

Sharpton added that it isn't fair to dig into Clark's cell phone and texts unless authorities dig into the police officers' texts to see who they were mad at and what they were up to, as well.

KTVU reached out to the DA's Office on Monday but didn't immediately hear back.

The relatives of Oscar Grant and Sahleem Tindle, both unarmed African-American men in Oakland who were killed by police, also attended the Sacramento news conference.

The two Sacramento police officers said that Clark was standing in a position in his grandmother's backyard, indicating to them that he was preparing to shoot them.

One officer described ducking back behind a corner of the house after thinking Clark had shot at him. He described the situation as "surreal" and said everything seemed to be moving in "slow motion."

The district attorney released an enhanced photo from an officer's body camera showing a flash of light from Clark's position near his grandparents' back door, which she said supported the officers' statements.

Schubert and Becerra said video from a police helicopter and independent reviews of Clark's official autopsy showed he was advancing toward the officers, contrary to an autopsy conducted for his family that said he was shot from behind.

The officers did not identify themselves as police, but both said they ordered Clark to stop and show his hands.

Both said during their interviews that they recalled Clark bring described in dispatch calls as a black male wearing black clothing or a black sweat shirt. Becerra's report said dispatchers did not describe the suspect's race but that a resident and a deputy in the circling helicopter said he was wearing a hooded sweat shirt.

The officers knew Clark was black by the time they were interviewed, Becerra's report says.

U.S. Justice Department officials announced they will conduct their own review to see if the officers violated Clark's civil rights.

The Associated Press contributed to this report.