Police Chief Kevin Treadway said his department is conducting an internal affairs investigation and asking the Northern Arizona University Police Department to conduct a criminal investigation.
"I am as concerned with what is depicted in the video as I know many others are. I've heard your concerns and the department is taking this incident very serious," said Treadway.
Wednesday night, after the video surfaced, Bonar was called in and placed on administrative leave. Bonar has been with the force just under three years.
Treadway said the officer reported that Marissa Morris kicked him and kneed him in the groin before he hit her. She claims that did not happen and said the officer had his hands around her neck before the video started recording.
She was arrested on suspicion of aggravated assault and resisting arrest.
The video shot from a home where Morris and her boyfriend were being evicted shows Bonar punching Morris. But the images taken from behind a railing show Morris and Bonar from the waist up and it is not clear from the footage whether she kicked or kneed the officer.
Treadway said Bonar was detaining the woman because he knew about warrants for Morris' arrest, but police later determined the warrants stemming from DUI cases were no longer active.
Bonar "was thinking the warrants were still in place," the police chief said. Morris is heard on the video saying she that there was no warrant for her arrest, and a female bystander says, "she doesn't have a warrant anymore."
Treadway said he learned about the Wednesday afternoon incident after a police department employee saw a Facebook video of the incident taken by a bystander. The video at one point shows Morris on a sidewalk with Bonar as he tells her she must cooperate so he can arrest her.
After Bonar punches Morris in the face, a male voice is heard saying, "You can't hit a girl like that!"
KGUN9'S sister station ABC15 spoke with Morris who said this was a "brutal attack."
"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. "Those warrants were done, and over with, I had done what I needed to do to take care of those, and I just got off the phone with pretrial services 20 minutes prior to this happening."
She said police "are sworn to protect, not hurt." Morris appeared before a judge Thursday who ordered her released pending a Dec. 6 preliminary court hearing.
"Why me, what did I do to deserve something like this?" she said. "I am not a bad person."
Sarah Erlinder, a Coconino County Public Defender's Office attorney who is representing Morris in her pending DUI case, said she had no information about the new case and could not comment on Morris' behalf.
"We owe Marissa, the family, and the entire Flagstaff community, the officer and the department, a full and complete investigation," Tredway said. "In the spirit of transparency, we are creating a standalone page, attach to our Facebook, where the original video, and additional video, reports, media reports, and applicable policies will be posted."
Morris said she has seen the video. "It is disturbing, I see it every time I move my arms or look at my face, or feel my face," she said.
Police say Bonar did not immediately activate his body camera when he arrived as "the contact quickly escalated" but did initially activate the camera when he arrived. He later reactivated the camera once the woman was placed in handcuffs.
"Officer Bonar's failure to activate the camera prior to the incident will also be addressed during the internal affairs investigation into his actions," Sergeant Cory Runge with the department said.