DeRay McKesson, one of the most prominent activists associated with the police reform protest movement, was arrested Saturday night in Baton Rouge, Louisiana, where he traveled earlier in the day to demonstrate in solidarity with residents angered by the recent death of Alton Sterling after an officer-involved shooting that was captured on video.

McKesson was taken into custody around 11 p.m. in what two fellow activists who witnessed it described as a physically violent arrest.

“The officers won’t give their names,” said Brittany Packnett, a co-founder with McKesson of the group Campaign Zero, a prominent activist collective. “He was clearly targeted.”

She later tweeted that 100 people were arrested in Baton Rouge. There was no immediate official confirmation of that figure.

Packnett said McKesson was using his smartphone to live-stream the ongoing protests when police began forcibly dispersing the crowds. As McKesson and a group of about eight people walked down the street, an officer approached him and told him that he had been “flagged” and that if he left the sidewalk again he would be arrested.

Moments later, she said, two officers forcefully arrested McKesson.

“They tackled him. One officer hit the top of his body and another officer the bottom,” Packnett said.

The altercation knocked the phone from McKesson’s hand, ending his live broadcast of the demonstration, she said.

Blurry video of the moments before McKesson was taken into custody provided to The Washington Post captures his verbal exchange with the officers.

“The police continue to just provoke people,” McKesson said after an officer yells to a group of people that if they step on the roadway they will be arrested.

Then an officer says the man in the “loud shoes” has been “flagged”: “You in them loud shoes, if I see you in the road, if I get close to you, you’re going to jail,” an officer can be heard saying on the video.

In response, Packnett says, “We’re on the shoulder. There is no sidewalk, sir.”

McKesson is known for wearing a pair of red Nike sneakers and a blue vest to all protests he attends.

The group was walking away from a protest and rally that had been dispersed, traveling alongside road traffic on a street that they said does not have a sidewalk.

Activists continued to talk as they walked up the side of the street. Moments later, an officer’s voice is heard.

“City police, you’re under arrest.”

“What?!” McKesson exclaims. “I’m under arrest y’all.”

Then the video and audio feed cuts out.

As Packnett and Johnetta Elzie, another prominent protester, tweeted in outrage, word spread quickly through the ranks of national police reform activists, who fear that McKesson was targeted deliberately and may be harmed in police custody.

In a text message from police custody, McKesson said he and 33 others were in custody together, wrists tied, and being taken to a police precinct.

News of McKesson’s arrest exploded on social media, with more than 100,000 tweets before dawn using the hashtag #FreeDeray. Many urged people to call Baton Rouge police and demand his release.

A police spokesman confirmed his arrest to The Advocate newspaper, but did not elaborate on potential charges and did not return a request for comment from The Post. As Saturday night became Sunday morning, there was no word on what charges McKesson might be facing. But a website for a local jail showed that McKesson was an inmate there as of Sunday.

McKesson called a close friend in Baltimore around 5:30 a.m. and told her he was in OK physical condition but did not know when he would be released, the friend told The Post.

(c) 2016, The Washington Post · Wesley Lowery