WATCH: 4 Arizona Police Officers Put on Leave After Video Shows Beating of Unarmed Man

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, 33 — 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.

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SOURCE: NBC News, Erik Ortiz