(CNN) Sacramento police officers shot and killed a black man in his grandmother's backyard because they believed he was pointing a gun at them, police said.
But investigators say they did not find a weapon at the scene, only a cellphone near the man's body.
The fatal shooting of Stephon Clark on Sunday night was recorded by two officers' body cameras and from a police helicopter; that footage was released Wednesday.
The videos show a brief encounter between police and Clark, lasting less than a minute, from the moment one of the officers spotted him in the driveway and yelled, "Hey, show me your hands. Stop. Stop."
In the dark, the two police officers chased Clark into the backyard of his grandmother's home.
"Show me your hands!" one of the officers yelled. "Gun, gun, gun."
Then police opened fire. Clark crumpled to the ground, momentarily tried to crawl before falling motionless as more shots erupted around him.
His death has caused outrage among residents who say the officers should be held accountable for his death. Police have said the officers fired only because they thought their lives were at stake.
As more police arrived at the scene, someone is heard asking "What did he have on him?"
An officer responded, "Like this, something in his hands. It looked like a gun from our perspective."
Minutes after the shooting, as more officers arrive on the scene, a voice is heard saying, "Hey, mute," and the audio on the body camera cuts off.
Clark's grandmother said she was inside the house when the shots were fired and saw him with an iPhone.
"He was right there dead. I told the officers, you guys are murderers, murderers, murderers," she told the Sacramento Bee.
The incident began on Sunday after 9 p.m., when Sacramento officers responded to a report that a man had broken car windows and was hiding in a backyard. The man was described as 6-foot-1, thin and wearing a black hoodie and pants, police said in a statement.
Officers arrived and were aided by a team in a Sacramento Sheriff's Department helicopter. Police said the helicopter personnel observed that the suspect had picked up a "toolbar" and broken a window to a residence. The helicopter team observed the man running and looking into another car, police said. The helicopter then guided officers to the man's location in the backyard of a home.
The camera from the helicopter showed a man running through a backyard and hopping a fence into another yard. The aerial footage captured the moment when two officers began heading toward him.
Officers arrived at the front yard and gave the man commands to stop and show his hands, according to police. The man immediately fled to the backyard, police said, and they pursued him.
At that point, the man "turned and advanced toward the officers while holding an object" extended in front of him, according to police.
"The officers believed the suspect was pointing a firearm at them. Fearing for their safety, the officers fired their duty weapons, striking the suspect multiple times," the police news release states.
The body camera footage is dark and shaky. The helicopter pivots, blocking the aerial view of Clark and the two police officers in the brief seconds leading up to gunfire.
The officers fired 20 times at Clark and he was hit multiple times, police told CNN affiliate KOVR. Officers then handcuffed Clark and began lifesaving efforts, according to police. He was pronounced dead at the scene.
The two officers involved in the shooting have two and four years' experience with the Sacramento police, and both have four years' prior experience with other agencies. The officers have been placed on paid administrative leave amid a use of force investigation.
Police said detectives canvassing the neighborhood found at least three vehicles with damage they say they believe Clark caused, as well as an adjacent residence with a shattered sliding glass door. Deputies in the helicopter witnessed him shatter the door, police said.
Stevante Clark, the victim's brother, told HLN that his brother "wasn't a thief."
"He was arrested before, but he's been different lately, he really changed his life. He was a people person who everybody wanted to be around. We came from underprivileged, broken homes, but he didn't care about nothing else but his kids."
Stevante Clark said on HLN that his priority right now wasn't a possible lawsuit or body camera footage, but focusing on Clark's two young children.
"I just want to make sure his kids go to school, my mom is good, and he gets buried in a way where we don't have to worry -- the nicest funeral," he said.
He said he and his mother did not plan to watch body camera video of his brother's shooting, but he expressed skepticism about the police version of what happened.
"They said he had a gun. Then they said he had a crowbar. Then they said he had a toolbar. Now I'm asking you, you've got a nice job, you sound pretty smart. What is a toolbar?" he said.
"If you lie to me once, I know you'll lie to me again."
The Rev. Al Sharpton has pledged his support for Clark's family and said he would be in California to help them fight for justice, according to a statement from his organization.
Sacramento Mayor Darrell Steinberg told reporters Thursday that Clark's death warrants a through review of the shooting, and of police policies and procedures.
"It is vital that we give voice to the pain in our community, especially the African-American community," the mayor said.
Steinberg said, "I feel the community's anguish." He also called for the public not to rush to judgment until an investigation is completed.
"Emotions are understandably high. People are anguished," he said. "I understand it and we understand it. I urge our community to remain peaceful."