The bystander video recorded Wednesday shows Flagstaff Officer Jeff Bonar and a Coconino County sheriff's deputy as Bonar tries to arrest a woman he believes has outstanding warrants.
Bonar, who has been a Flagstaff officer for three years, knew Marissa Morris from an encounter one month ago and at that time there were two warrants for her arrest.
He came to the house to assist the deputy on a separate matter -- an eviction.
Morris argues with Bonar on the video and tells him, "You've gotta have a warrant."
Bonar tells her to stop fighting with him.
After she says, "You cannot arrest me until I know I have a warrant," Bonar throws a straight right hand that hits her near her left eye. Her head snaps back, but she remains standing.
In his report, Bonar says Morris was high on some drug and "exerted an impressive amount of strength for a women her size." He says she kneed him in the groin and legs several times.
He said the punch and several others were "distraction blows, with very minimal force." Only one punch is seen in the video and Morris' hands and legs are not visible.
As it turns out, Morris had warrants in October, but they had been settled.
The video was shot by a resident who lived in the home with Morris, police say. Bonar didn't turn his body camera on until after the punch. It is unclear whether the deputy had a body camera.
Bonar wrote he turned off his body camera when he thought he was no longer needed in the eviction. Then he recognized Morris, but forgot to turn the camera back on as they faced off.
Morris told CNN affiliate KNXV
that she was attacked.
"He came after me, pretty much tackled me to the ground, and told me I was under arrest for a warrant that I did not have," she said.
Morris told the Arizona Daily Sun that she didn't assault the officer.
"I did not put my hands on him or hit him or strike him or kick him or anything of that manner," she told the Flagstaff-based newspaper
. "I did nothing to abuse or hurt him. I was trying to protect myself."
CNN left a voice mail seeking comment at a phone number listed for Bonar.
Police say they became aware of the situation when video was posted on Facebook.
"I'm as concerned with what is depicted in the video as I know many others are," police Chief Kevin Treadway told reporters Thursday. "I have heard your concerns and the department is taking this incident very seriously."
Internal affairs will determine whether Bonar violated policy during the incident. An outside agency, the Northern Arizona University Police Department, is conducting a criminal investigation, Treadway said.
Morris was booked Wednesday evening on suspicion of aggravated assault and resisting arrest.
The chief said that based on a booking photo and a jailhouse interview, Morris didn't have any injuries.
Flagstaff police policy
says: "Officers shall use objectively reasonable force in response to resistance given the facts and circumstances perceived by the officer at the time of the event to accomplish a legitimate law enforcement purpose. Given that no policy can realistically predict every possible situation an officer might encounter, officers are entrusted to use well-reasoned discretion in determining the appropriate use of force in each incident."