PORTLAND, Ore. (AP) — A protest medic who works as an intensive care unit nurse at Oregon Health and Sciences University filed a lawsuit Thursday in federal court against the city of Portland and the police officer who arrested him.

Tyler Cox claims his constitutional rights were violated Aug. 31 when Officer Thomas Clark tackled him after police declared a riot, Oregon Public Broadcasting reported. Video shows Cox was moving with the crowd away from officers.

The 27-page complaint alleges Clark punched Cox in the face and head “a minimum of five times.”

The Multnomah County District Attorney’s Office has been investigating Clark and considering criminal charges.

Last month, District Attorney Mike Schmidt announced an assault charge against another police officer for allegedly hitting a protester in the head from behind. Schmidt referred another case to the Oregon Department of Justice for possible charges. That contributed to the police bureau’s entire Rapid Response Team resigning, though they kept their jobs within the police bureau.

Cox suffered a traumatic brain injury that’s improved but not fully resolved, his attorney Joe Piucci told OPB.

Police charged Cox with assaulting a public safety officer and three misdemeanors. Those charges were dropped.

Portland police Sgt. Kevin Allen said he couldn’t comment on the pending litigation. City Attorney Robert Taylor also declined comment on the suit, The Oregonian/OregonLive reported.