Jennifer Gonnerman on the Philadelphia District Attorney, who is reinventing the role of the modern prosecutor. : Until Larry Krasner entered the race for District Attorney of Philadelphia last year, he had never prosecuted a case. He began his career as a public defender, and spent three decades as a defense attorney. In the legal world, there is an image, however cartoonish, of prosecutors as conservative and unsparing, and of defense attorneys as righteous and perpetually outraged. Krasner, who had a long ponytail until he was forty, seemed to fit the mold.