The incident occurred at a gas station station in Decatur on June 4. The officer had gone to the Chevron in response to a complaint about the woman begging for money from customers.
The video posted on YouTube doesn't show what led to the incident.
It starts with a tense scene in which the woman, identified as Katie McCrary in a police report, is on the floor as a male police officer beats her with his baton. The officer had filed a Use of Force report after the incident and had been cleared following an internal affairs investigation.
In light of the new cellphone video, the DeKalb County Police Department said in a statement Monday: "Now that the Department has this new evidence we have reopened the investigation and will determine whether the incident is consistent with policy and the law."
The incident marks another controversy that has risen over the scrutiny of police tactics.
The identity of the police officer in the Decatur incident hasn't been released.
In his incident report dated June 5, the police officer said, when he arrived at the gas station, McCrary "attempted to push me out of the way and walk out of the door."
McCrary allegedly tried to walk past the officer again and told him she was a federal agent, according to his incident report. More words were exchanged and McCrary "reached out and grabbed my badge," and after being warned not to touch him, she "grabbed my vest and radio," according to his incident report. He said he used his baton on her legs, forearms and "one strike inadvertently struck the side of her head as she was moving around."
The cellphone video starts with McCrary lying on the floor with her arms and legs in the air as she attempts to kick at the officer who is standing. He swats her multiple times with his baton.
"Hey, Katie. Stop resisting!" yells an unknown man in the store. "Stop resisting."
The officer strikes her several more times as the woman squirms on the ground.
At one point, he places the baton on the back of her neck and pins her down with his knee on her back. When she grabs his baton, he says twice, "Let it go, or I'm going to shoot you."
"No. Please don't shoot her," a bystander says.
Near the end of the video, the officer places her in handcuffs.
McCrary asks repeatedly, "What did I do? What did I do wrong?"
DeKalb County Police Department said in a statement, "The narrative in the officer's report appears to be consistent with the video."
The officer wrote in his incident report that he took McCrary to DeKalb County Jail, "where she was refused and deferred to Grady Memorial Hospital for further evaluation." He noted she had a half-inch cut on her shin and a welt on her forearm. She was later released by the hospital.
McCrary was charged with obstructing or hindering law enforcement officers. She was given a criminal trespass warning at the request of the convenience store manager, police said.
CNN is attempting to reach McCrary or her lawyer.
CNN affiliate WGCL
reported McCrary is currently in jail for an unrelated charge. One man who says he knows McCrary told WGCL that she's often seen at the store asking for money and alluded to mental health issues.