Johnny Martorano. Whitey Bulger. The Boston Strangler. The Craigslist Killer. What do they have in common? All are the subjects of true-crime books from Boston-area writers: Howie Carr, Casey Sherman, and Michele McPhee. Together, they’ll freak out those assembled at the Somerville Theatre when they appear this Saturday as part of a night of true crime tales.?xml:namespace>