Police arrested out prominent Black Lives Matter activist DeRay McKesson during a peaceful protest last night in Baton Rouge, Louisiana, and McKesson livestreamed his arrest on the Periscope app.

Baltimore Native and Black Lives Matter activist, Deray McKesson, was arrested last night in Baton Rouge, LA. pic.twitter.com/wP4k3iHvXh

— DC Maryland Virginia (@DMVFollowers) July 10, 2016

The Baton Rouge protest was one of many that took place in cities across the nation, demonstrating over the police killing of Philando Castile in Minnesota and Alton Sterling in Baton Rouge.

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The arrest took place after a police officer warned McKesson about walking over the line in the road. There was no sidewalk to march on, and it did not appear that McKesson stepped over the line into the road. McKesson was arrested a few minutes later and his Periscope stream was taken over by a fellow protester.

.@deray officially charged with "simple obstruction of a highway of commerce." See affidavit of probable cause. pic.twitter.com/0zScUQ9cs2

— Yamiche Alcindor (@Yamiche) July 10, 2016

The NYT reports:

As word of Mr. McKesson's arrest spread on Twitter, where he has more than 460,000 followers, #FreeDeray began trending, with thousands tweeting out messages of support as well as phone numbers for the Baton Rouge police department to demand his release.

The Louisiana National Lawyers Guild, which is providing legal support to protesters, set up an online fund-raiser aimed at raising money to bail out Mr. McKesson and several other protesters arrested in Baton Rouge.

State Police officials defended the arrests of Mr. McKesson and others as a matter of public safety.

McKesson had been posting to Twitter all evening. A few of his tweets: