Prominent Black Lives Matter activist DeRay Mckesson arrested at Alton Sterling protest in Baton Rouge _lowres

Police arrest activist DeRay McKesson during a protest along Airline Highway, a major road that passes in front of the Baton Rouge Police Department headquarters Saturday, July 9, 2016, in Baton Rouge, La. Protesters angry over the fatal shooting of Alton Sterling by two white Baton Rouge police officers rallied Saturday at the convenience store where he was shot, in front of the city's police department and at the state Capitol for another day of demonstrations. (AP Photo/Max Becherer)

BATON ROUGE, La. (AP) — A federal judge has ruled that Black Lives Matter is a social movement that can't be sued over an officer's injuries during a protest following a deadly police shooting in Baton Rouge last year.

A Baton Rouge police officer sued Black Lives Matter and DeRay Mckesson, a prominent activist in the movement. But U.S. District Judge Brian Jackson ruled Thursday that Black Lives Matter is not "an entity of any sort," and like the tea party or civil rights movement, it can't be sued.

The judge also concluded that Mckesson "solely engaged in protected speech" at the July 2016 demonstration where someone threw a rock at the officer. The protest followed the death of Alton Sterling, a black man fatally shot by a white police officer.

The officer in the suit, identified only as John Doe "for his protection," sought damages over a claims he was struck in the face by a piece of concrete or similar rock-like item hurled at officers.

A lawsuit brought by representatives of injured East Baton Rouge Parish Sheriff's Deputy Nick Tullier has also named Black Lives Matter and Deray Mckesson — among others — as defendants. 

That lawsuit filed on July 7, alleged the defendants, along with others, "incited violence against police." It also claims the activists' criticism of law enforcement led directly to 29-year-old Gavin Long's July 17 attack. Another sheriff's deputy — Brad Garafola — and two Baton Rouge Police officers — Matthew Gerald and Montrell Jackson — were killed in the attack. 

The Black Lives Matter movement began around 2013 to protest the fatal shootings of black people, primarily by police.

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