"Photo is agonizing for me to see," Ellison wrote on Twitter. "My son is PEACEFULLY protesting w/ hands up; officer is shouldering gun. Why?"
The picture was originally published by the Minneapolis Star-Tribune before being re-posted online on Wednesday night, amid protests against police use of force in the death of 24-year-old Jamar Clark. It can be seen in full below.
Police removed demonstrators on Wednesday after they gathered near the city's north police precinct, where Clark was shot early on Sunday morning. Local activists have said that Clark was handcuffed and unarmed at the time. Clark died on Monday night.
The two officers involved in the encounter, Mark Ringgenberg and Dustin Schwarze, have been put on administrative leave.