LOS ANGELES (CNN) -- The video starts with a man swinging his arms at police officers outside a Los Angeles homeless shelter.
An officer tackles him to the ground, and three others try to subdue him. At least one pulls out a Taser and tries to shock the man.
"Drop the gun!" a voice yells.
Seconds later, five gunshots ring out, prompting shock and screams from bystanders.
"Why did y'all shoot that man?" one witness yells. "Y'all got (him) tased. Why did you y'all shoot that man?"
The fatal shooting Sunday on Los Angeles' Skid Row sparked renewed outrage online over what some consider unnecessary lethal force by police. The shooting took place near the Union Rescue Mission, a homeless shelter in a neighborhood rife with poverty.
Anthony Blackburn, a bystander who shot the video, said he started filming with his cell phone after officers surrounded a homeless man in front of his tent on a city sidewalk.
"I had my phone out, you know, videotaping the whole thing 'cause we've been hearing on the news about police brutality," Blackburn told CNN affiliate KABC-TV. "I just wanted to film it and just make sure everything was all right. But I ended up seeing a tragedy."
Los Angeles police Commander Andrew Smith said the man was suspected of robbery. When officers tried to arrest him, he started fighting with them.
Smith said police tried to shock him with a Taser, but that didn't work. After the man reached for an officer's gun, three officers fired at him.
"I don't know what they found on this individual," Smith told CNN. "Obviously he didn't have a firearm."
Witness Tonya Edwards told CNN affiliate KTLA-TV she knew the man who was shot, describing him as a homeless person who had "a lot of mental issues."
Another witness, Yolanda Young, told KTLA the man "had three Tasers on him."
"He was down, but then he jumped up, like he was juiced up, and then he started swinging at the police and they were fighting him back. ... They shot him five times," Young said.
While police struggled with the man, another tussle broke out when one officer lost his baton. A bystander picked it up.
"Get my stick! Get my stick!" the officer yelled as other officers tackled the woman.
Blackburn said fellow witnesses were bewildered by the shooting.
"The young black officer that shot him, he went over to the crowd, telling everybody back up in an aggressive way," he told KABC.
Late Sunday, a crowd gathered at Los Angeles' Pershing Square to remember the man shot, known as "Africa" and "Brother Africa."
Los Angeles police said they will review video from various sources during their investigation of the shooting. The Los Angeles County district attorney's office will also launch an investigation, police said.
Los Angeles police senior lead Officer Deon Joseph, a longtime Skid Row patrol officer profiled by CNN in January, wasn't working when the shooting happened. But he said, "It looks like the officers had to make a tough call."
"The system is really failing the mentally ill, as well as the cops who have to contact them," he told CNN's Ann O'Neill through Facebook. "I'm seeing so many more new faces in Skid Row. And many of them have serious issues. It's really tough out there."
CNN's Sara Sidner reported from Los Angeles, while Holly Yan reported and wrote from Atlanta. CNN's Janet DiGiacomo and Christine Sever contributed to this report.