Katharine Miller says it started off peaceful and quickly turned violent.
Video shows Miller kneeling on the ground being maced in the face, protesting the very thing she says she suddenly found herself a victim of.
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"All of a sudden people started screaming and sprinting. There was clearly more gas behind us and there was just nowhere to go," she said.
Desperate to breathe from the tear gas, protesters scaled the embankment on the highway.
Miller spotted Diamonik Hough kneeling on the ground as police moved in to disperse the crowd on the Vine Street Expressway.
"All I could think was this person is going to get murdered. We've all seen this video. So I jumped down and knelt in front of him," Miller says.
"My memory goes black at this point. The last thing I remember is a police officer walking towards us," said Miller.
The officer in the video sprays Miller, pulls down the goggles of the woman next to her before spraying her. He then confronts Hough, who also hit with rubber bullets while trying to dodge the pepper spray.
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"There was no reason for the blatant use of force," says Riley Ross with Mincey Fitzpatrick Ross, LLC.
Ross and his firm is representing more than a dozen protesters.
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"What about the argument that these protesters did not have any permit or any type of approval to be on the highway?" asked reporter Christie Ileto.
"Protesters had nowhere to go but to run up the hill and escape over the fence. If you wanted them to leave the highway, escort them off the highway," Ross said.
It's not clear if the officer in the video is with the Pennsylvania State Police or with the city, but the department hired an independent consultant to review its protest response, which the Philadelphia police union is calling an "independent second guesser."
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"Did they do the right thing? It's difficult just going by that short snippet of video that I saw," said Steven Nolan, a former Philadelphia lieutenant who is now a use-of-force expert.
Nolan says the clip is a snapshot of a bigger picture.
"What was needed for the use of force for that moment, what we're individuals doing for officers to use excessive force in which they did?" said Nolan.
"If you could say anything to that officer what would you say?" asked Ileto.
"Why is your first reaction to three people kneeling on the ground to incapacitate them instead of getting us off the highway. We would have gotten off the highway," said Miller.
The Philadelphia District Attorney's Office says it is aware of the incident and is investigating photos and videos from the scene. It also created a feed for residents to submit information. Reports are up from the public are up 300%.