Newly released footage from Arizona appears to show another example of police using undue force on an unarmed citizen.

The surveillance video opens with a Mesa police officer exiting an elevator onto an apartment complex's fourth-floor deck. A man — later identified as Robert Johnson, 35 — comes into view. He leans forward on a railing and checks his phone.

About three minutes later, four officers surround Johnson while he appears to be on his cellphone. They talk to him and he shifts his body against a wall. Then they grab him, knee him in the gut and throw several punches to his head and body until he slumps to the ground.

They place him in handcuffs. Later, an officer shoves his head into the elevator door.

The 20-minute clip released publicly Tuesday is part of an internal investigation that led the officers to be placed on administrative leave, Mesa Police Chief Ramon Batista told NBC affiliate KPNX.

While the incident occurred May 23, Batista said he only learned of it a week later.

"This in no way represents the whole work that is done everyday," Batista said. "They're human beings and certainly at first glance this looks like a mistake, it doesn't look right. And it's my job, it's our job to collectively investigate and find the answers to this."

Johnson was not being investigated at the time, but was at the complex while his friend allegedly tried to get into an ex-girlfriend's apartment, police said. Authorities were called as part of a domestic dispute.

Johnson, who did not have any weapons on him, is facing disorderly conduct charges, KPNX reported.

The video does not contain audio, although police claim Johnson was argumentative and refusing commands to sit down. Another man can be seen in the video sitting against a wall.

"There is no explanation that can justify that level of force," Johnson's pastor, Andre Miller, told reporters. "When you look at the video, even after he was unconscious, he was still struck."

Johnson's attorney, Benjamin Taylor, couldn't immediately be reached for comment Wednesday. He said in a statement Tuesday that his client was cooperative and being peaceful against the wall.

"The misconduct of these officers would have gone unnoticed if it had not been captured by surveillance videos at the apartment complex where the assault occurred," Taylor said. He wants the police department to hold the officers accountable and "develop a law enforcement culture that meets community and constitutional norms."

The Mesa Police Association, which represents the officers, said in a statement that the video does not provide the full context of the encounter because there is no audio.

"It is important to understand that any use of force, when viewed, is difficult to watch and never looks 'good,'" the union added.

As a result of the incident, the Mesa Police Department has changed its use-of-force policy so that officers can only hit people in the head or face if they become physically violent, officials said. Previously, the policy could be interpreted that it was acceptable for an officer punch someone even before they turned violent.

CORRECTION (June 15, 2018, 7:09 p.m. ET): An earlier version of this article misstated Robert Johnson's age. He is 35, not 33.