They were chasing him AFTER he shot the first guy in the back and head.
Rosenbaum was shot multiple times, possibly once in the back by another shooter. They were chasing him prior to Rosebaum being shot.
An autopsy conducted by the Milwaukee medical examiner's office indicated Rosenbaum suffered multiple gunshot wounds, according to the probable cause statement.
One shot was fired into his right groin, fracturing his pelvis. Another shot to Rosenbaum's back perforated his right lung and liver. He also suffered a gunshot wound to his left hand, a superficial gunshot wound to his left thigh and a graze wound to the right side of his forehead, according to the narrative.