The San Bernardino, California sheriff released new body-camera footage of the fatal police shooting of 15-year-old Ryan Gainer, who was holding a gardening tool.

The Saturday killing of Ryan, who was autistic and having a mental health crisis, sparked national outrage and escalating criticisms, prompting the head of the department, Sheriff Shannon Dicus, to show reporters additional footage during a Wednesday press conference. The sheriff also revealed that it appeared two deputies on the scene had fired three rounds at Ryan.

Dicus repeatedly defended the deputies’ use of lethal force, at one point referencing Ryan’s “large stature” – a comment that drew immediate backlash from local civil rights advocates.

Audio of 911 calls and partial clips first released on Monday indicated that a relative called police to report Ryan was breaking things in their house and had attacked his sister. At one point, the caller said Ryan had said he was “going to run away”.

The first 15-second video released showed one deputy arriving at the home in Apple Valley, east of Los Angeles, to find an open front door. A man inside could be heard saying, “He’s got a stick in his hand,” and soon after, Ryan appeared holding the gardening tool, identified as a 5ft hula hoe.

The deputy at the door shouted: “Get back … you’re going to get shot.”

The newly released footage captured the moment of the shooting as Ryan moved toward the deputy, although the deputy was running away from him and facing the other direction. The shooting was not visible on the video. When the deputy and his camera turned back to Ryan, he was lying on the ground.

Footage from another deputy, who was the second to arrive, captured that deputy shooting Ryan from a distance. Ryan appeared to be holding the tool over his head when he was shot by both deputies. The footage, however, is grainy. Both deputies shot Ryan less than a minute after arriving, and within roughly seven seconds of him appearing in their view. Dicus did not name the deputies.

The footage captured Ryan’s family members screaming in the aftermath, saying: “Why did you shoot him? … Why didn’t you tase him? Where are your Tasers?”

Dicus said he did not believe there was an opportunity to use a stun gun or other weapons: “The use of a Taser in this situation with the amount of time or the use of pepper-spray would not have been something we would have been able to react to quick enough. Ultimately we have to stop this problem … law enforcement officers are not required to be hit over the head with something. What happens when they get incapacitated? … The deputies followed through with what their training protocols are.”

He later said: “Certainly juveniles can be dangerous. He is large of stature. He is physically fit.”

DeWitt Lacy, a civil rights lawyer representing the Gainer family, criticized the remarks in an interview after the briefing, saying: “Across America, we’ve often heard of the ‘Herculean Black man’ and ‘wild savage’ that needs to be put down. We won’t allow Ryan’s name and image to be concocted or depicted in that way.”

Lacy added: “This kid was not a savage, and no one was in imminent danger of death or great bodily injury at the time of the shooting.

“They used the deadliest action they could do because of this myth of the Black man, the Black monster … He was just a kid. It’s the responsibility of law enforcement to deal with these types of situations without killing us.”

Dicus, the sheriff, said the department had been called to the home to assist with Ryan on five previous occasions, and had previously taken him to mental health facilities without using any force. He said he could not say whether the deputies who shot him were aware of that history when they responded on Saturday, and he criticized the local mental health care system for failing to take care of his needs.

The family has also said that the sheriff’s department was slow to render aid to Ryan after shooting him. The footage showed the deputies waiting roughly a minute to approach Ryan while he is on the ground and while the family is screaming, saying: “He’s dying … Why would you do that?”

“Ryan was lying there, moaning in agonizing pain and impending death while they took no action,” Lacy said after watching the footage. After a minute, deputies moved to try to treat his wounds, though the department cut out audio during the treatment, Dicus said, to protect the investigation.

Ryan was a cross-country runner who aspired to be an engineer, his family said. Community organizer Sennett Devermont, whose group Always for the People Foundation advocates for families of people killed by police, has been working with Ryan’s relatives and friends and posted old footage one of them shared of Ryan speaking in a TikTok video: “To all the viewers, make sure you have a great day, be the spark, and make sure to spread kindness,” the teenager said.

Devermont called for the deputies to be terminated and face criminal charges. “It’s imperative that officers who are this irresponsible are held accountable. Without accountability, I don’t know how we can expect this to stop.”