The worst part about DeVito's fictional character "Bobby Ciaro" is that he's loyal to Hoffa to the very end. Nobody was loyal to Hoffa to the very end, except maybe his immediate family. Even his foster son, Chuckie O' Brien, was likely in on his murder.

Bobby Ciaro would have been more plausible if it were him that who shoots Hoffa at the end, or if he's involved in setting him up. In that case, he could have been based on Rolland McMaster, Hoffa's Teamster muscle man who eventually turns on him, O 'Brien, or a combination of both. Neither of these two are portrayed in the film, while both played pivotal roles in Hoffa's life, and possibly his death.