As I understand it, he "sold illegal cigarettes" and had been picked up for it at least 5 times. Cops are human. Worse, they believe in "upholding the law" the way JW's believe in upholding their Truth. When the cops saw him on the street and figured he was up to his old tricks, they snapped, and it was fatal for him.
Was it "right"? No. Is it understandable? Yes. Some parents do the same thing; try to deal with the misbehaving kid all day then snap and over-punish. But is it really the cop's/parent's "fault"? What responsibility belongs with the guy/kid?