A police officer in Madison, Wisconsin has gunned down a 19-year-old who was unarmed.

Police Chief Mike Koval said Saturday that Tony Robinson was not armed when he was killed by 12-year veteran Matt Kenny, according to a CNN report. Koval said the revelation would make the investigation into the death “more complicated.”

Kenny had used deadly force in the past, shooting to death a man in 2007, according to the chief as quoted in the report. He was exonerated of wrongdoing in that death and even received a commendation for his efforts, with police ultimately concluding that the victim had committed “suicide by cop.”

Kenny encountered Robinson Friday evening when Kenny arrived at a home in Madison to respond to a disturbance call. Robinson allegedly attack him.

Robinson had pleaded guilty to violent crimes before, including an armed robbery just last year.

Although Robinson was unarmed, police say that Kenny was assaulted. However, Koval declined to go into Robinson’s criminal history, calling it “wholly inappropriate” considering the situation.

The shooting prompted protesters to march on City Hall chanting “black lives matter,” as protesters had done in the killings of Michael Brown in Missouri and Eric Garner in New York.

Koval asked for people to remain calm, acknowledging that it was “understandable that the reaction at the scene and of some of our citizens is extremely volatile, emotional, and upsetting,” but said that people should exercise restraint.

Police initially responded to a report that a black man was jumping on cars and yelling, a man who was later identified as Robinson, according to the report. The dispatcher indicated that Robinson was unarmed but had attacked on of his friends and had tried to strangle someone. Koval said that Kenny had heard commotion inside an apartment and forced his way in, which is when Robinson assaulted the officer.