During a news conference, Houston Police Chief Art Acevedo presented video footage from body cameras that showed 27-year-old Nicolas Chavez, who had already been shot and was bleeding, kneeling on the ground and grabbing a stun gun that had been dropped when the four officers shot him.
Acevedo said although Chavez had picked up the stun gun, the officers had plenty of time to back up and take cover. Chavez was already injured, having been hit by gunfire earlier in his standoff with police. Officers had also fired bean bag rounds and stun guns at him before he was killed.
"Quite frankly, it's inexplicable to me when they had plenty of opportunity to back up and continue to be doing what they were doing for them to stay the line and shoot a man 21 times," Acevedo said. "I cannot defend that."
The footage was shown during a news conference that also included Houston Mayor Sylvester Turner, who was visibly upset by the shooting.
Note: ABC13 chose not to carry the live release of the footage due to its strong graphic content.
WATCH: Mayor Turner on officers' firings: 'You have to call a ball a ball and a strike a strike'
Moments after the news conference, Harris County District Attorney Kim Ogg said the case against the officers is being presented directly to a grand jury.
"I met with the mother, father and wife of Nicolas Chavez to listen to their concerns and personally assure them that our Civil Rights Division prosecutors will conduct a thorough, independent review of all the evidence in his death. Once we complete our review, we will present the case directly to a grand jury. That grand jury will determine whether the Houston Police officers who shot Nicolas Chavez were justified or whether they committed a crime," Ogg said in a statement.
Those fired were identified as: Officer Patrick Rubio, who had been with the department since May 2018; Officer Luis Alvarado, with the department since March 2019; Officer Omar Tapia, with the department since March 2019; and Sgt. Benjamin LeBlanc, with the department since October 2008.
READ THE OFFICIAL LETTERS OF 'INDEFINITE SUSPENSION'
Earlier in the day, and shortly after the officer firings were announced, the Houston Police Officers' Union blasted the department's actions.
"This unjust and deplorable decision by Chief Acevedo has sent a shock wave through HPD, even if you deescalate, retreat, follow policy, training and the law...you will still lose your job as a Houston Police Officer," union president Joe Gamaldi tweeted Thursday.
He added that the officers were forced to shoot Chavez when he pointed the stun gun at them.
"It was clear ... these officers did not want to shoot Mr. Chavez and did everything in their power not to," said union president Joe Gamaldi.
RELATED: HPD chief Art Acevedo says he's investigating deadly officer-involved shooting in east Houston
Chavez was killed after officers responded to a call about a suicidal person who was armed and running into traffic in the 800 block of Gazin Street in northeast Houston.
Chavez's shooting followed a 15-minute confrontation with police. Chavez's family has said he had a history of mental illness.
WATCH: ABC13's Jessica Willey report from April 2020 on the shooting investigation
In a video presentation of the body camera footage that was narrated by Acevedo, portions of 911 calls made the night of Chavez's shooting can be heard where callers tell operators that a man is running around and "having a mental breakdown."
In the video footage, officers can be heard telling Chavez, "Hey buddy, hey bud, we're here to help you, man" and "just relax. No one is shooting" and "we're trying to help you man."
Chavez, who can be heard cursing at officers, could be seen wildly flailing his arms and legs. Officers fired bean bag rounds from shotguns at Chavez and deployed their stun guns, but it had little affect on him.
At one point in the video, an officer said Chavez had a knife. Officers told him to put it down. Investigators later determined that Chavez had a piece of metal that he used to cut himself.
WATCH: A walk-through of the body camera footage
Before Chavez was fatally shot, two officers had fired three times at him when Chavez had come toward officers, injuring him. Acevedo said those discharges of officer weapons were justified
"The action being taken today does say in our city, we hold everyone accountable," said Mayor Sylvester Turner.
Gamaldi said the fired officers used every non-lethal option available to them to subdue Chavez, but that he refused to surrender.
"These officers were distraught over having to take a life out there," said Doug Griffith, the union's first vice president.
While Griffith said the shooting was found to be justified by the city's independent police oversight board, Acevedo disputed that claim. Acevedo declined to comment further, citing confidentiality.
Activists had earlier called on Acevedo to release body camera footage from Chavez's shooting.
Chavez's death was the first of six fatal shootings involving Houston police over several weeks in April and May.
The Associated Press contributed to this report.