Nineteen-year-old Tony Robinson was not armed when a Madison, Wisconsin, police officer fatally shot him, Police Chief Mike Koval said Saturday.

"We have to be clear about this," Koval said. "He was unarmed. That's going to make this all the more complicated for the investigators, the public, to accept, to understand … why deadly force had to be used."

The officer who killed Robinson, 12-year department veteran Matt Kenny, had used deadly force before, shooting and killing a man in 2007, the chief said. Kenny was exonerated of any wrongdoing and even received a commendation, the chief said, adding that the incident was "concluded to be a suicide by cop" situation.

Robinson was shot after allegedly assaulting Kenny, who was responding Friday evening to a reported disturbance at a Madison residence, Koval said.