Ryan B. Carlsen finds the greatest personal reward in the cases people haven’t heard about.Two years ago, the Cook County assistant public defender was representing a young man charged with aggravated vehicular hijacking. Had it gone to trial, his client was looking at possibly 21 to 45 years in prison.But Carlsen was able to show in pretrial proceedings that his client was misidentified by the hijacking victim. He had an alibi and was wearing different clothes at the time of his arrest than the ones described by the …