20th Century Studios and Hulu unveiled a new trailer for “Boston Strangler,” a true-crime retelling of the infamous Boston Strangler murders in the 1960s starring Knightley, 37, as Boston Record-American reporter Loretta McLaughlin, who investigated the string of murders for the newspaper. The film follows Loretta McLaughlin (Keira Knightley), a reporter for the Record-American newspaper,…